Leviathans

The Leviathans (also called The Old Ones, Chompers, or Levis for short) are primordial beings that served as God's very first beasts. Thus, they predate angels, humans, and the soul itself. The creatures proved to be too hungry and destructive, so God created Purgatory and locked them inside. They were inadvertently released when Castiel opened Purgatory and absorbed all the souls inside in order to defeat Raphael.

Upon their release, the Leviathans attempted to conquer the North America and place themselves as the new dominant species on the planet, subsequently harvesting the human race as their primary and abundant food source while eliminating all other competitors and threats to their food.

This attempt to subjugate mankind was thwarted through the combined efforts of hunters, angels, demons and even monsters but was ultimately stopped by Dean Winchester and Castiel after they managed to defeat the Leviathans leader and architect of their plan: Dick Roman. According to Crowley the Leviathans themselves disbanded after Dick's death and are scattered but their actual fate is unclear.

Biography
After his existence appearing in The Darkness, God created the Leviathans. These beasts were among God's earliest creations, predating angels and humans. Whereas Death "personally found them entertaining", God worried the beasts would, as Death put it, "chomp the entire petri dish" as they proved to be too strong, too hungry, and too destructive. Some time after he bound the Darkness, God locked away the Leviathans in Purgatory - which Death reveals as being specifically created to contain Leviathans. In addition, after locking the Leviathans up, God devised a means of killing the Leviathans should they ever escape Purgatory. When he had the Word of God tablets created, God made one for the Leviathans in case they ever escaped, putting instructions for the weapon on the tablet as well as a warning about them. The most powerful Leviathan ended up as their leader and was the only one they ever had since the beginning of time according to Crowley, a dependency that was another weakness of theirs as without their leader, the Leviathans would be left without direction and lose all sense of cohesion.

Season 7
When Castiel cracked open Purgatory and imbibed the souls found in there, he also unknowingly absorbed the Leviathans. After some time, they began manifesting in him and ordered him to let them out.

Due to their uncontainable power, Castiel's vessel began deteriorating, until he could no longer hold it together. Coming to Sam and Dean for help, he, with the help of Dean and Bobby, opened the door to Purgatory again and hurled the souls back in. Shortly after Castiel had got rid of the souls and his body was repaired, he realized the Leviathans were still inside him. Unable to hold up against them, he finally succumbed and the Leviathans surfaced, telling Dean that Castiel was now "gone". Relishing their newfound freedom, they inform Dean that now they are going to have fun.



However, they are soon forced to leave Castiel's body due to the vessel being unable to handle them. So, using Castiel, they head to a water reservoir and, using the water, spread to the population, taking new vessels, thus possessing multiple people. They then break into two distinct groups; those who can control their hunger and proceed to observe the human world and those who act careless in their feeding and thus draw attention.

Two Leviathans meet in a park to discuss the current situation. The Leviathan possessing Edgar reveals to the Leviathan in the girl's body that he is here because the leader heard about the careless feeding of some of the others and is angry that it has drawn human attention. He tells her to get the Leviathan in the area in line because their leader "hates bad news".



They realize they can't leave Sam, Dean and Bobby alone, and decide to get rid of them. This leads to Edgar burning Bobby's house down and attacking Sam and Dean. Sam and Dean manage to get away and Leviathan set their feelers out. They begin tracking the Winchesters, flagging their credit cards. Chet manages to catch up with Sam and Dean, but is stunned by Don Stark. Sam and Dean put the body in the Impala.

Later, two Leviathans impersonate Sam and Dean and go on a bloody rampage; turning the brothers into public enemies and to draw them out of hiding. Thanks to Bobby discovering the Leviathans' weakness to Borax, they are able to deal with their doppelgangers and again convince the world they are dead. The Leviathan disguised as an FBI agent comes to collect the bodies, but the sheriff lies to them. The Leviathan returns later and eats the Sheriff and his daughter.



Elsewhere Crowley meets with the leader of the Leviathans who is impersonating businessman Dick Roman. Crowley attempts to secure an alliance with the Leviathan but Roman sees through Crowley and tells him he would rather "swim through hot garbage than shake hands with a bottom feeding mutation like you." The creature explains that it sees demons as lesser than humans, whose only use is a food supply. Roman tells Crowley not to bother him again and warns him that, if not currently occupied with other matters, the Leviathan would wipe demons out in a heartbeat.

It is later revealed that the Leviathans are lacing hamburgers sold at restaurants with a chemical that turns humans into complacent, overweight drones, ready for the slaughter. Dick Roman, however, shuts down this project when a small number of humans are turned into cannibalistic creatures.

Later, while investigating cursed objects in Portland Oregon, Dean and Sam discover that Leviathan realtor Joyce and her assistant George, are acquiring properties from local owners, and killing those who refuse to sell. In the confrontation that follows, Sam and Dean decapitate Joyce with help from George who plans to eat her in order to kill her. Afterwards, George reveals that the Leviathans are planning on building a research facility, in order to find a cure for cancer. "We're only here to help".

The ghost of Bobby later reveals to Sam and Dean that the Leviathan aren't here to hunt humans, but to harvest them as cattle - hence explaining their desire to "cure" humans of diseases. Sam and Dean enlist the help of hacker Charlie Bradbury to infiltrate Dick Roman's headquarters, and they are able to intercept a package which turns out to be a stone tablet.



When Dean cracked the stone containing the tablet the Winchesters stole from Dick Roman, Kevin Tran was awakened as a prophet of the lord. Sam and Dean enlist Kevin to decipher the tablet, which is revealed to be one of the Words of God, and a "emergency note" concerning the Leviathan. It states that the Leviathan can be killed with the Bone Of Righteous Mortal Washed In the Three Bloods of Fallen. Castiel provides some of his blood, as he is a fallen angel. Dick Roman discovers the identity of the prophet Kevin Tran and that he has the power to read the Word of God. He orders Edgar to capture the prophet, which he does by posing as a detective and questioning Kevin's mother. As chance would have it, two angels deliver Kevin to his mother and directly into Edgar's hands. Edgar easily kills the angels and takes Kevin, proving that his kin is stronger than the latter.

The Leviathan purchase SucroCorp and begin lacing the high fructose corn syrup additives in processed foods with their DNA-altering chemicals. The Leviathans are able to quickly spread the additive and humanity starts to become mindless just as they originally planned. Dick also does a series of interviews promoting himself and his plans with SucroCorp.

After capturing Kevin Tran, and reading the tablet translation, Dick Roman sends Edgar to kill the Alpha Vampire and get his blood. Edgar travels to the Alpha's hideaway and the two discuss the Leviathan and vampire relationship. The Alpha worries about the death of other vampires, especially after Sam and Dean told him that the Leviathans are purposefully making the food poisonous to them. Edgar states "mankind is a limited resource" and reveals the Leviathans intent to wipe out any other monster with a taste for human flesh. However, Sam and Dean break in and Sam decapitates Edgar. Edgar's visit has the opposite intended effect: now knowing that the Leviathans have betrayed him and owing Sam and Dean his life, the Alpha gives them the blood they need without a fight.



In the Season 7 finale Survival of the Fittest, the Leviathans expand their plans to not only fatten and harvest the human population, but to also exterminate those humans with undesirable qualities (people who are too thin, vertically challenged, too smart, or have hemophilia). They intend to do this through a dairy cream engineered to kill only people with low body mass. However, these plans are foiled when Dean and Sam Winchester break into SucroCorp, and Dean stabs Dick Roman with their weapon, killing the Leviathan leader, though Dean and Castiel are transported to Purgatory in the process.

After the death of their leader, the Leviathans are left confused and disorganized which, according to Crowley, is because Dick is the only leader they ever had from creation. With Dick dead, the Leviathans are little more than ordinary monsters. Crowley informs Sam that they have to keep them from reorganizing and that he has an army of demons outside SucroCorp ready to dispatch all the remaining Leviathans inside. As Crowley puts it, they've become "just another monster" that's hard - but not impossible - to kill.

Season 8
In the Season 8 premiere We Need To Talk About Kevin, Dean proves to Sam that he is not a Leviathan among the other tests he performs and does the same to Sam. Later, after finding Kevin Tran and he shoots them with a squirt gun, Dean appears to assume it is Borax as he informs him as well that they are not Leviathans. All the Leviathans influence appears to be gone by this time one year later as people are no longer dumbed-down as they were before the assault on SucroCorp and Sam and Dean eat regular food without apparent worry or mention of the food additive.

In What's Up, Tiger Mommy?, Castiel reveals that he abandoned Dean in Purgatory as he feared that the more powerful monsters there, including the Leviathans that are still in Purgatory, would come after him and he didn't think Dean was safe. However, Dean doesn't care that the Leviathans may be after Castiel and convinces Castiel to work with him and Benny to get out.



In Blood Brother, while arguing with Dean and Benny, Castiel senses Leviathans nearby and the three run, but are attacked by two Leviathans. Dean decapitates one, but the other gets the drop on Castiel and nearly kills him before Benny decapitates it.

In A Little Slice of Kevin, Castiel reveals that the last thing he remembers in Purgatory before mysteriously escaping is Leviathans chasing him. In a flashback, as Dean and Castiel head for the portal out, two Leviathans appear and attack them. The Leviathans knock Dean down and fight Castiel, preventing him from using his powers on them. They overpower him, but Dean decapitates one from behind as its distracted and then decapitates the other one as Castiel holds its head in place.

In Pac-Man Fever, its briefly suggested that a Leviathan was responsible for a djinn's murders, showing that at least some Leviathans are still out there somewhere.

Season 10
During The Werther Project, Dean has a hallucination that he is in Purgatory once again under the influence of the Werther Box. A Leviathan attacks him, but before it can kill him, it is decapitated from behind by Benny.

Characteristics
According to Death, the Leviathans were the first beasts created by God. Death describes them as "clever" and "poisonous". He also says he personally found them "entertaining". The Leviathan were known for their power and ravenous hunger and their purpose of satiating it by finding and taking sustainable food sources. Because of this, God was worried they might "chomp the entire petri dish." and locked them in Purgatory.

Based on remarks made by both Edgar and the Alpha Vampire, Leviathan are just as old as Eve and are related to her in some way. This is supported by the Alpha's claims that the Vampires, who are Eve's children, originate from Leviathans - to which Edgar responds, "barely". Furthermore, when the Alpha points out that he is a son of Eve, Edgar replies that he knew Eve and that she was a "mutt", implying that Eve may be a Leviathan hybrid or mutation. Edgar, however, expressed scorn to both Eve, whom he claimed to know and described as a whore, and her monster creations. Leviathans despise all other species and enjoy flaunting their superiority over their enemies. In general, Leviathans regard humans as little more than cattle and food. They also consider seven billion to be a limited resource demonstrating the masses they intend to consume. They do, however, have some respect for certain individuals, such as Charlie Bradbury and Kevin, who possess a certain "spark" that the Leviathans are unable to copy. Their leader seems to admire these individuals for their ingenuity and progress, as well as their history of warfare and violence. Despite this, even Dick views this as "cute" and considers them all as food. Leviathans also consider demons to be lower than humans and garbage and would kill them all simply on principle if they weren't preoccupied with other things to do. They also hate the monster races sired by Eve, viewing them as competitors who are using up their food supply, to the extent where they genetically engineer their human complacency drug so that it poisons every monster as a side effect. Leviathans are also cannibalistic, eating other Leviathans for their failures (or just being annoyances). Their leader is known for his cruel punishment, known as "bibbing," in which he forces a Leviathan that failed him to eat itself. In general, Leviathans believe every other species to be inferior to them and consider themselves invincible, believing it impossible for humans, demons or angels to kill them. Because they are able to kill practically all other species, they consider themselves the top of the food chain and fear nothing but their superiors.

Though chaotic, it is established that Leviathans have some sort of hierarchy, with several of them taking orders from their leader, Dick Roman. Under Roman's command, there are head Leviathans, like Edgar and Joyce, who in turn have authority over other Leviathans. Dick Roman orders several Leviathans to hunt down those in their group who have been feeding indiscriminately and to deal with the Winchesters and their allies. Their hierarchy seems to operate entirely through strength and fear, as Dick talks about clawing his way to the top, and George doesn't even attempt to challenge his superior on his own and fears her greatly. In general, the Leviathans in authority have an easy time keeping the rest of them under control. They show no real loyalty for each other and will betray their superiors if it is in their best interests and obey their superiors out of fear rather than loyalty. George disobeyed and even turned against his superior, Joyce, in Out With The Old. Only Dick Roman himself seems to command absolute respect and loyalty from the Leviathans species as a whole and is feared by all of his subordinates (as he bibs or eats any who disobey or fail him). However, with Dick dead, the Leviathans hierarchy is destroyed as they have no-one to turn to as Crowley points out they have only ever had one leader. Without Dick, the Leviathans resort to acting like regular monsters, although Crowley warns Sam that the remaining Leviathans may try to regroup unless Sam and other hunters prevent them from doing so.

On Earth, they take serpent-like shape underwater. Once within a vessel, Leviathans are able to shapeshift without taking a new one (provided they can acquire DNA). They seem to change their hosts biological structure, as they replace the vessels blood with their black goo. While in a host, they can dislocate the jaw and reveal a mouth full of large teeth and a forked tongue. While they can devour almost anything, they seem to prefer humans to all others. They can also have particular tastes. For example, Chet liked to eat his victims with melted cheese sauce as "everything tastes better with cheese." Dick Roman sometimes had his meals barbecued. Leviathans are also capable of eating human food, such as hamburgers and salads, but they find it disgusting. At least some of them enjoy the taste of other Leviathan, as before consuming his subordinate Dick questioned "Why would I waste a perfectly good meal?"

As seen on the episode Blood Brother, their true form in Purgatory, as perceived by humans, looks like a ball of black goo, much like the substance of their injured vessels on Earth. In this form, they have incredible mobility, as they have shown the capability to fly and land anywhere with a noticeable force, before taking humanoid form. Although this form still possesses the powerful jaws, the leviathans may choose when to reveal them. It should be noted that this may only be how they can manifest in front of human like entities, like angels manifesting in vessels in front of humans, as they were originally created long before humans. Their original form has never been described before they were locked in Purgatory.

Powers and Abilities
"You know, Leviathan can kill angels. That's the reason why my father locked them in Purgatory. They're the piranha that would eat the whole aquarium."

- Castiel

As some of God's first creations, Leviathans are very powerful beasts, more powerful than most other creatures, and able to kill and/or eat just about everything else. It is notable that despite the Leviathans' status as much older than angels and their ability to kill the celestials with relative ease, Leviathans have yet to show any form of magical or psychic abilities besides flight when in Purgatory. Leviathans are also capable of wiping out all demons, as claimed by Dick Roman--a claim that forced the demon Crowley to flee and organize his demons against the beasts by allying with the Winchesters a second time. Even the angels are powerless against Leviathans as Castiel stated that his entire garrison had been killed by the beasts. This makes them rather unique as they are able to defeat creatures who possess far more abilities than they do. Before the Leviathan threat could be ended, it took the hunters, angels, demons and even other monsters to forge loose alliances with each other and combine their efforts.


 * Powerful Jaws - Leviathan possess massive, retractable jaws that are immensely strong and serves as their primary weapon and way to feed. Their jaws can rip open almost anything they bite into, including humans, angels, demons and various other creatures - even other Leviathan. Using this ability apparently significantly alters the users face, such removing their eyes and nose to make room for their jaws.
 * Invulnerability - The only way for a hunter to kill a Leviathan is with a Bone Of Righteous Mortal Washed In the Three Bloods of Fallen. While use of witchcraft, Borax, decapitation or extreme physical force can disable and weaken them temporarily, they will recover from the damage in a matter of seconds to hours, depending on the extent of damage. Edgar recovered unharmed after a car was dropped on him and Chet showed no pain when connected up to a car battery or injected with acid. More powerful Leviathans such as Dick and Edgar are less susceptible to Borax damage and can regenerate their wounds even quicker than others of their kind. Besides these methods, they are virtually indestructible.
 * Immortality - Being creatures much older than souls and angels, the Leviathan are immortal, in a variety of senses, in that having an ageless lifespan, meaning they simply do not age, and can not be killed by but one mean, devised by God himself. Death reveals that the Leviathans were one of God's first creations, being before angels and humans. Leviathan are immune to literally every angelic and demonic weakness, and as stated above, can only be killed by that one way devised by God.
 * Possession - Much like demons, Leviathan can take over a human host's body and mind by a touch, though unlike demons the process alters the host biologically and appears permanent. Many of them can possess a single host at once, as demonstrated with Castiel (though this proved to be unstable). While in Castiel's soul empowered body they were able to briefly gain control over his vessel and slaughter a large number of people at a campaign office. Not only can they possess an already occupied vessel, but they can eradicate the creature that is possessing the host they are invading, as shown when they kill Castiel and gain control over his vessel.
 * Shapeshifting - Through physical contact with just one strand of DNA, Leviathan can instantaneously shapeshift their vessel into that person's form, transforming into the person they are in contact with. They can also use hair instead of physical contact to assume a person's identity. Soon after changing, they commonly eat the original person. They are also able to take on the memories of not only those they possess, but those they shapeshift into, allowing them to access their form's memories and skills (even complex ones such as severing vocal cords). The leviathan mimicking Sam also absorbed all his memories from his time in Lucifer's cage but unlike Sam his psyche was not phased and he found it simply irritating. Unlike most other shapeshifters, they have the ability to mimic a human's specific clothing as well, making it even easier to impersonate people. They can also shapeshift into creatures of a different species such as vampires. However, it would seem they cannot copy Prophets as Dick Roman kept Kevin Tran alive to decode The Word of God rather than simply copying him and absorbing his memories. They are sometimes unable to copy a person's skills to their fullest as seen when Dick opted not to do so with Charlie. Leviathan are also unable to copy other Leviathans, as evidenced by the fact that Dick had to use a piece of the original Dick Roman to make his duplicates. Only Eve, the Alpha Shapeshifter and the archangels could demonstrate advanced shapeshifting as the Leviathans did.
 * Super Strength - Leviathan are immensely physically stronger than humans, monsters, demons and top-level spirits. Leviathans are even stronger than angels and can overpower them with ease. Edgar was able to casually kill two angels from Castiel's former garrison (in which Castiel held the title of "captain") and effortlessly restrained a vampire with one hand, shortly before ripping its head off with his bare hands. Even when Chet had been crippled by a spell it still took numerous chains to restrain him. They are even able to overpower seraphs as demonstrated with Castiel, as he has shown to fear them greatly and have overpowered him at least twice. However, Castiel was also able to hold his own against two Leviathan who teamed up, and his physical strength was enough to push them back and hurt, long enough for Dean to behead them. However, he was unable to do any lasting damage. Castiel was also no match for the Leviathan leader Dick Roman though when he caught him by surprise, he was able to briefly restrain him. Similarly, the Alpha Vampire was able to shove Edgar with his strength but Sam predicted correctly that Edgar would inevitably win and "eat him alive". Furthermore, Ghosts (such as Bobby) are able to knock down Leviathan such as Dick Roman and Pete but was also unable to do any lasting damage.
 * Super Intelligence - Leviathan are very adaptable as they were able to grasp full understanding of modern technology and systems despite being in Purgatory since the dawn of time. Leviathan were able to make a food additive that cured cancer, AIDS, and other human diseases that would make humans less desirable "cattle." They also produced other additives that would kill all other non-leviathan beasts, and that made humans compliant as well as one that killed people with undesirable traits (low body mass, hemophilia, high IQ). In addition, they were able to track the Winchesters' location with complex computer algorithms, something vampires, demons and even angels failed to do or be aware of, resulting in Bobby calling them a Mensa monster. Dick Roman was capable of accurately assessing an individual's skills and noted that his kind was not always capable of replicating a human's abilities to the full extent of their potential. Dick Roman was also well-versed in constructing terms and conditions to avoid any loopholes in making a deal with Crowley.
 * Super Stamina - Leviathan have unlimited stamina and never tire, however they do get hungry but cannot starve to death. However, the stronger leviathan have a better control of their hunger, allowing them to blend more easily in the society. Others combated this weakness by taking up positions in hospitals so they could feed regularly without raising suspicion.
 * Super Speed - Leviathans can move at incredible speeds, displayed when two Leviathans eat a swimming team.
 * Enhanced Senses - Leviathan have far superior senses compared to humans. Edgar, for example, was able to tell that a small puddle of blood had come from Dean. Dick was also able to sense that it had dropped ten degrees when Bobby (as a ghost) was present in the room. Despite this, they are unable to see certain entities such as ghosts, but they can sense angels and demons.
 * Supernatural Concealment - At least one high ranking Leviathan managed to conceal his true form from other creatures with supernatural perception. This allowed the Leviathan to take on the two angels by surprise, before killing them with his poisoned blood.
 * LeviathanKillsAngel.jpgVenomous Blood - It is shown by Edgar that Leviathan are able to instantly kill angels (and probably other creatures if not anything excluding themselves) by sticking their fists into their chests and injecting them with black Leviathan blood. Victims of this ability swell up grotesquely, their blood vessels darken, and black blood spews from their mouths as they die. Castiel's garrison were also slaughtered by the Leviathan.
 * Angelic Power Negation - Leviathans are able to block an angels powers through their physical presence. Edgar was capable of negating by an attempted counterattack by an angel, shortly before killing the angel. This ability also extends to Seraphs as while in Purgatory, Castiel was unable to teleport in the presence of Leviathan because they were too close and were preventing him using his abilities. However, he was earlier able to teleport into the presence of Dick Roman and other Leviathan while on Earth when they did not expect him and the two angels Edgar killed teleported into his presence while he was concealed. This indicates that the Leviathan have to consciously block angelic power for it to work.
 * Flight - In their true form in Purgatory, Leviathans have shown the ability to fly and land anywhere with extreme speed and force. In this state, they appear as meteors composed of a thick, black ooze.
 * Regeneration - Leviathan can heal from virtually every form of injury. Edgar was able to recover without a scratch after being crushed by a car and both Edgar and Susan healed completely after being shot in the head at point blank range. They can even survive decapitation and will reattach their heads to their bodies after a short time (though they will be inactive until they reassemble). Even while they can be pushed back by seraphs and ghosts, they can endure almost any hit without receiving damage. They are also able to regenerate from the damage inflicted by borax and high ranking Leviathan such as Dick or Edgar can heal from such damage instantly.

Weaknesses
Leviathans are extremely hard, but not impossible, to kill, as only two methods are known to destroy them, and even when killed on Earth, its essence will survive and return to Purgatory. Prior to their arrival on Earth, they considered themselves invincible and were not aware of anything that could even hurt them. However, they possess a few weaknesses which enable their opponents to harm or incapacitate them, albeit with difficulty. Although the Leviathans are the very first creations of God and are powerful in their own right, they themselves have a few weaknesses, little of which can kill them, but can all injure them.

Weapons, Spells and Rituals

 * Witchcraft - While it's unknown if witchcraft can kill a Leviathan it has been shown that it can incapacitate them temporarily. It should be noted that this was done by a very old and powerful witch, Don Stark, who stunned the low-mid ranking Leviathan Chet unconscious with ease and in a blink when caught off-guard. The spell he improvised lasted for days, leaving the Leviathan in a helpless state which might be evident due to their lack of defense against magical means. However, it still took several chains to restrain Chet and Don advised the brothers to drop the Leviathan down a bottomless pit implying he at least couldn't kill him.
 * Decapitation - By removing a Leviathan's head, the Leviathan is rendered immobile and unable to act. However, the head must be kept at a significant distance from the rest of the body, or it will eventually reattach itself.
 * Borax - Borax is extremely caustic to Leviathan, weakening them and eating their flesh much like holy water does to demons, giving hunters and other beings enough time to decapitate them or escape from them. Higher-ranking Leviathan, like Dick Roman are able to endure and recover from the chemical's effects much quicker than lower-ranking Leviathan.
 * Rigid Hierarchy - A major Leviathan weakness is their over reliance on just one leader, Dick Roman. According to both The Word of God and Crowley, if Dick is killed, the Leviathans lose all cohesion and revert into ordinary monsters. However, Crowley warns Sam that they may eventually try to regroup if he and other hunters do not prevent them from doing so.

Beings

 * Ghosts - Leviathan can be overpowered by ghosts, as seen when the ghost of Bobby attacks Dick Roman. Leviathan are unable to see ghosts as they are beings that exist strictly on the physical plane. However, ghosts cannot seriously hurt Leviathans as both recovered quite quickly from Bobby's attack with no damage.
 * Castiel - Due to Castiel being their original vessel, Castiel is able to see past their vessels, see their true forms and tell each Leviathan apart, no matter what form it takes.
 * Higher Tier Angels - Castiel, a Seraph was able to briefly hold his own against a Leviathan even in their domain, however he was not able to smite them. He was also unable to defeat them unaided. In a straight fight, Castiel was no match for Dick Roman, the Leviathan leader and the strongest of the species, but was able to restrain him for a moment after catching him by surprise.

Weapons and Events

 * Bone Of Righteous Mortal Washed in the Three Bloods of Fallen - According to The Word of God, the bone of a righteous mortal (as good and light as the Leviathan are hungry and dark) washed in the three bloods of the fallen (a Fallen Angel, the ruler of fallen humanity, and an Alpha) is the only way for a hunter to kill the Leviathan. When fatally stabbed with this weapon, the Leviathan will bleed black blood, then start generating ripple-like pulses through the air, then finally explode in a shower of black goo. It is also implied by Crowley and Castiel that this weapon, once used to kill a Leviathan, can drag its essence and anyone in the immediate vicinity to Purgatory.
 * Death's Scythe - It can kill almost anything.
 * The First Blade - Being powered by the Mark of Cain and therefore the Darkness, the blade can kill anything.
 * Cannibalism - Leviathan can kill other Leviathan by eating one another, or by eating themselves. (The latter is a punishment known as "bibbing").

Beings

 * Primordial Entities - The Darkness, God, and Death can effortlessly kill them.

Alternate Future
In his final moments in Time After Time, Chronos, the god of time, mentioned to Sam and Dean that in their future, "black goo" (referring to the Leviathans) was everywhere; implying that in the future Chronos saw, the Leviathans took over and covered the whole Earth.

Known Leviathans

 * Eve (deceased) - She was at least part leviathan, implied by The Alpha Vampire and Edgar.
 * Dick Roman (deceased) - The head Leviathan.
 * Edgar (decapitated) - Dick's right-hand man and a high ranking Leviathan.
 * Joyce Bickleebee (decapitated) - Another relatively high ranking Leviathan.
 * Annie/Dr. Gaines (deceased) - A mid-level Leviathan subordinate to Edgar.
 * Susan - Dick's personal assistant.
 * George - Joyce's assistant.
 * Royce - A Leviathan who worked in Dick Roman's lab at SucroCorp.
 * Chet (decapitated) - A lower ranking Leviathan assigned to hunt down and kill Sam and Dean.
 * Leviathan Sam and Leviathan Dean (decapitated) - Two Leviathans assigned to impersonate Sam and Dean and frame them for a spree of murders. Leviathan Sam admitted to having eaten his schizophrenic brother.
 * Agent Valente - A Leviathan disguised as an FBI agent assigned to track down Sam and Dean.
 * Leviathan Pete - Charlie's supervisor; formerly under the guise of a human named Tarrell.
 * Victor (deceased) - Leviathan responsible for picking up a package at the airport.
 * Chef Fieri (mentioned) - presumably Dick Roman's personal chef.

Appearances

 * Season 7
 * Meet The New Boss
 * Hello, Cruel World
 * The Girl Next Door
 * Shut Up, Dr. Phil
 * Slash Fiction
 * How To Win Friends And Influence Monsters
 * Death's Door
 * Out With The Old
 * The Girl With The Dungeons and Dragons Tattoo
 * Reading Is Fundamental
 * There Will Be Blood
 * Survival of the Fittest


 * Season 8
 * Blood Brother (Flashbacks of Dean's time in Purgatory only)
 * A Little Slice of Kevin (Flashbacks of Dean's time in Purgatory only)


 * Season 10
 * The Werther Project (Hallucination)
 * Season 11
 * The Devil in the Details (mentioned only)
 * Alpha and Omega (mentioned only)

Lore
In the Judeo-Christian tradition a Leviathan is a giant sea monster, described in the Book of Job Source. The Talmud Baba Batra 75b states that the archangel Gabriel will be the one who slays the Leviathan. Other legends say God will slay the beast. In hindsight, researchers believe that Leviathans were a title for ancient sea deities from mythologies, and that God's declared superiority over those is to strengthen the idea of monotheism over the polytheism in the biblical nations. Death also refers to the Leviathans as "The Old Ones", a term used by H.P. Lovecraft in the Cthulhu mythos to describe ancient powerful alien beings who come to Earth. A race called the Old Ones also features in Stephen King's Dark Tower Series,in The Power of Five novels by Anthony Horowitz and also in The Vampire Diaries books were the Old Ones are exremely old vampires like Klaus. In Binsfeld's Classification of Demons, Leviathan is the name of Envy, one of the Seven Deadly Sins. The Demon Leviathan, is very high in Hell's hierarchy and said one of the four demons obedient to Lucifer. The Demon Leviathan, is responsible for cases of demonic possession, and it's said be extremely difficult to exorcise.

While the name Leviathan comes from Job 41, the creatures have more in common with Kabbalah's stories. Genesis 1 mentions the creation of man and woman before discussing Adam and Eve. Some Jewish texts suggest a race of intelligent beings were created before humans. It goes on to suggest that these beings were so terrible that God destroyed them, but that their spirits lived on as demons.

In nowadays Hebrew, Leviathan (or Leviathanim in plural) is the Hebrew name for a whale.

Trivia

 * According to the book "Supernatural: The Official Companion, Season 7", Leviathans are primordial creatures of the sea that evolved to possess other animals so they could live on the land.
 * Castiel and others refer to the Leviathan species as Leviathan (singular), while Death, Sam and Dean usually refer to the species as Leviathans (plural).
 * They are the first beings to appear in more than 10 episodes during their inaugural season.
 * The Leviathan are one of the most dangerous, indestructible antagonists to appear on the show.
 * They were referred to as "The Old Ones" by Death. This may be a reference to the ancient creatures described by H.P. Lovecraft, who had previously created a portal to Purgatory, where the Leviathan were once imprisoned.
 * The Leviathans are sometimes referred to as "chompers" or "Levis" by other characters in the series. Dean also referred to one of them as Pac-Man, due to the video game character's large mouth and eating habit.
 * Despite Leviathans not having souls, whatever comprises them as a being returns to Purgatory upon their death. (This was confirmed by Death, and shown with Dick Roman when he, according to Castiel, returned to Purgatory after Dean and Castiel killed him.)
 * Upon "riding Castiel into Paradise," the Leviathan essentially absorbed all of Castiel's memories of Heaven, and the one getting a DNA sample off Sam bears all of his "Cage-match scars" unfazed.
 * Frank Devereaux suspected that Gwyneth Paltrow and Fred Savage were possessed by Leviathan.
 * According to VFX I/O Coordinator Adam Williams, the "gorilla-wolves" that Dean and Castiel first encounter in Purgatory were visual effect models made for the Leviathans that they ultimately decided not to use, and re-purposed as "gorilla-wolves."
 * It is unknown if the Pagan Deities are stronger than the Leviathans.