Near the beginning of time, God created the Leviathans, the first monsters. However, they were insatiably hungry to the point that God feared that they would consume all of his other creations so he created Purgatory to lock them away forever.
After the Apocalypse was averted, the demon Crowley and the angel Castiel made a deal to find Purgatory and split all the souls found there between them in order to secure Crowley's position as King of Hell and to allow Castiel to defeat the archangel Raphael in the war they were involved with each other. After over a year of searching, the partners were able to find a way to open Purgatory, but Castiel betrayed Crowley and took all of the souls for himself, using their power to kill Raphael. Declaring himself the new God, Castiel rampaged across the Earth, causing both miracles and mayhem, unaware that when he took in the monster souls of Purgatory, he also took in the Leviathans. After the Winchesters and Bobby Singer bound Death in an attempt to kill the out-of-control Castiel, he warned them all about the threat the Leviathans posed, but Castiel was too arrogant to take him seriously. After the Leviathans briefly took control of Castiel and made him slaughter a senator's campaign office, Castiel finally realized the Winchesters and Death were correct and agreed to return all of the monster souls to Purgatory. While Castiel succeeded, he remained unaware that the Leviathans managed to hang on inside of him. The Leviathans took control of Castiel and used him to attack the Winchesters and Bobby before noticing that Castiel's vessel was starting to fall apart under the weight of holding them all. Retreating into a nearby reservoir, Castiel's body imploded, killing him and allowing the Leviathans to escape into the world.
Following their escape, the Leviathans began taking individual vessels of their own and searching for sources of food. To this end, one Leviathan posed as a surgeon at Sioux Falls General Hospital to steal organs from people while Edgar was sent to destroy Bobby's house and kill the Winchesters and Bobby who the Leviathans knew would try to stop them. While the fight left the Winchesters injured enough to go to the hospital, they both survived and temporarily defeated Edgar who they mistakenly believed to have been killed in the fight. At the same time, Bobby encountered the Leviathan masquerading as Dr. Gaines after being warned of the threat by Sheriff Jody Mills and was unable to hurt him. The Leviathans quickly learn of the Winchesters presence at the hospital and chase them, but Bobby is able to get them out of the hospital to safety in Rufus's cabin to recover while the Leviathans abandon the hospital. Over the next few weeks, hunters encounter the Leviathans and their activities, but they are unable to find a way to defeat them.
To track down the Winchesters, the Leviathan leader Dick Roman has a Leviathan named Chet who is posing as a credit card company employee use the Winchesters aliases, gleaned from the mind of Castiel, to hunt them down. Chet is eventually able to track the Winchesters down successfully after a case involving two witches and attacks them. The Winchesters are unable to defeat Chet, but witch Don Stark incapacitates him with a spell, allowing the Winchesters to capture Chet for study by Bobby to find the Leviathans weaknesses.
As Bobby studies Chet, Dick changes tactics and has two Leviathans pose as the Winchesters and go on a cross country murder spree to get law enforcement involved and try to force the Winchesters out into the open. After learning of how the Leviathans are tracking them from Chet, the Winchesters go to Frank Devereaux who provides them with new identities, information on their doppelgangers activities and on who's advice the Winchesters hide the Impala to help avoid detection. Bobby is eventually able to determine with the accidental help of Jody Mills that borax burns Leviathans like acid and decapitation incapacitates them permanently as long as the head is kept away from the body. Bobby passes this information along to Dean and then disposes of Chet's head and body separately with Jody's help, permanently defeating Chet. After being arrested in Ankeny, Iowa for their doppelgangers crimes, Dean defeats them with the help of Sheriff Osborne who fakes their deaths for FBI agents Morris and Valente. Afterwards, Valente reveals himself to be a Leviathan and kills the sheriff and his daughter before informing Dick of the situation. Dick chooses not to try the same tactic again and declines an offer by Crowley to work together.
Using his new identity as Dick Roman and his control of Richard Roman Enterprises, the Leviathan leader begins working on turning humanity into the perfect "herd" for the Leviathans, starting by having Dr. Gaines work on a food additive that makes those that eat it fat and mindless. However, this additive, distributed through Turducken sandwiches at Biggerson's restaurant, causes some people to turn into "hyper-adrenalized cannibals" that start attacking other people. This draws the attention of the Winchesters and Bobby, causing Dick to force Dr. Gaines to bib himself for the attention it draws to them, killing the Leviathan doctor. Dick captures Bobby as he runs surveillance on Dick's operation, leading to the Winchesters launching a rescue mission for Bobby. Bobby discovers the Leviathans plan from Dick's notes, but is shot in the head while escaping and dies soon afterwards, devastating the Winchesters. Unknown to anybody, Bobby chooses to remain behind as a ghost to continue to aid in the fight against the Leviathans.
Following Bobby's death, Dean becomes obsessed with finding and killing Dick Roman to avenge Bobby and hires Frank Devereaux to help with the search for information. Frank discovers Dick's buying of a field in Wisconsin, but is unable to determine what he's building there even with the help of surveillance run alongside Dean. On an unrelated case months later, the Winchesters find two Leviathans, Joyce Bickleebee and her assistant George buying up property and killing those who won't sell to build something else. With the help of George, the Winchesters defeat Joyce who George promises to eat in order to kill her completely. George explains that while he doesn't know what's going on in Wisconsin, the Leviathans are building a research center to cure cancer and claims that they are just there to help. Confused by this new information, the Winchesters travel to Frank's trailer to find it trashed and signs of a struggle, causing them to come to the conclusion that the Leviathans have caught up to Frank and killed him.
A few weeks after Frank's apparent death, Sam discovers that Dick is funding archeological sites all over the world, but the Winchesters are unable to determine what Dick is looking for. Having gained the ability to become visible, Bobby's ghost fills the Winchesters in on Dick's plan which he had learned before he was killed. Bobby explains that the Leviathan food additive is fattening humanity up for being eaten while also making them docile by lowering their intelligence. Bobby tells them that Dick has now bought a lot of restaurants and other places to help spread his food additive and ensure his plan's success. Bobby goes on to tell them that the next phase of Dick's plan is to cure humanity of all the diseases that afflict it such as cancer, the real reason for the cancer research center George had told them about.
At the same time, Dick tasks hacker Charlie Bradbury to hack Frank's hard drive in hopes of the Leviathans being able to learn what Frank knew about the Winchesters and their activities from it. The drive automatically sends out an email alert to the Winchesters who travel to Chicago to get it back before Dick can learn anything useful off of it. After about a day of work, Charlie manages to hack into the drive but reads it before giving it to Dick and learns of the existence of the Leviathans and the threat they pose. While initially disbelieving, Charlie witnesses a Leviathan replace her boss Pete and realizes that its true. Returning to her apartment, Charlie meets the Winchesters who explain the whole situation to her and enlist Charlie's help to raid Richard Roman Enterprises for Frank's drive and to hack Dick's emails to learn what his archeological digs are looking for. Charlie is able to erase the hard drive and help the Winchesters steal the object that Dick is after. After failing to stop the Winchesters from escaping with Charlie, Dick eats his subordinate Victor for his failure.
After stealing the hunk of clay Dick was after from him, the Winchesters break it open to reveal the Leviathan Tablet, turning Kevin Tran into a Prophet to read it. Opening the tablet also awakens Castiel who was resurrected by God after his death at the hands of the Leviathans but went insane after taking on Sam's Hell scars to save his life. Called in by Meg after Castiel wakes up, the Winchesters visit Castiel who identifies the Leviathan tablet as the Word of God to them but is not much help otherwise. Kevin is drawn to the tablet and after getting caught trying to steal it, discovers he can read the tablet and it talks about the Leviathans. The group then comes into conflict with angels led by Hester culminating in Meg killing Hester to protect Castiel. After Hester's death, the angels agree to allow Kevin to translate the tablet first before taking him away, but Edgar kills his angel escort and kidnaps Kevin and his mother.
After the angels depart, Sam discovers that the Leviathan tablet describes a weapon that can kill Leviathans and that they need a Fallen Angel's blood as the first ingredient. Castiel supplies them with the needed blood before departing. Dick also learns of the weapon by forcing Kevin to translate the tablet for him and sends Edgar to stop the Alpha Vampire from interfering. With the help of Bobby, the Winchesters determine they need Crowley's blood and the blood of an Alpha for the remaining two bloods for their weapon. After being summoned, Crowley refuses to help until they get the other ingredients for the weapon, but does give them a clue on where to find the Alpha Vampire, the only known surviving Alpha. They also learn that Dick has now acquired SucroCorp and is using it to spread his additive in the form of high fructose corn syrup, adversely affecting people all over now. The Winchesters are able to track down the Alpha Vampire who believes the Leviathans are on his side until he comes under attack by Edgar. The Winchesters defeat Edgar and the Alpha Vampire recognizes that they are on the same side and willingly gives them his blood for the weapon. The Winchesters then raid the grave of Sister Mary Constant, a nun they believe to be righteous enough to fit the criteria for their weapon. However, unknown to them, Dick summons Crowley into a devil's trap and makes a deal with him to give the Winchesters the wrong blood.
Not trusting Crowley to keep up his end of the deal, Dick uses the arm of the real Dick Roman to have a bunch of his subordinates take on his form to confuse anyone attacking him. Shortly after they discover this through security cameras, Sam has to stop Bobby, now a vengeful spirit from attacking Dick using a maid he is possessing. The Winchesters then try to summon Crowley for his blood, but fail to reach him before Meg returns with Castiel who reveals that the Leviathans have slaughtered his entire garrison. Crowley arrives and informs the Winchesters of his deal with Dick, but gives them the right blood as he wants Dick dead as much as they do. Crowley also informs them that Castiel holds the key to defeating the Leviathans. Meg eventually explains that as Castiel was the Leviathans original vessel on Earth, he possesses the ability to tell them apart no matter what form they take and can tell which one is the real Dick Roman. However, in his insane state, Castiel is unwilling to help fight as he sees himself as bad luck. After the Winchesters complete the weapon and burn Bobby's flask to put him to rest, Castiel has a conversation with Dean that leads to him agreeing to help them attack Dick and the other Leviathans.
With Castiel now agreeing to help, he, the Winchesters and Meg launch an all-out attack on SucroCorp to kill Dick and defeat the Leviathans. As part of their plan, Meg crashes the Impala into SucroCorp's giant glass sign, drawing out three Leviathan guards who are unable to harm her with their guns as she's a demon. Using borax and a machete, Meg dispatches the guards before being captured by two of Crowley's demons. As Meg distracts the guards, Sam, Dean and Castiel sneak into the building undetected. Sam is able to rescue Kevin who informs Sam of a deadly new additive Dick has added to coffee creamer to kill people with undesirable traits. On Kevin's insistence, Sam reluctantly agrees to blow up the lab rather than get Kevin to safety. After finding a few fake Dick Romans, Castiel is able to locate the real one in the SucroCorp lab and he and Dean teleport in and dispatch Royce before facing off with Dick. After a brief standoff, Castiel attacks Dick but is thrown into a wall. While Dick is distracted with Castiel, Dean stabs him with the weapon to no effect. As Dick taunts him over this, Castiel sneaks up behind Dick and restrains him long enough for Dean to stab him through the neck with the real weapon, revealing that the previous one had been a trick to catch Dick off-guard. The weapon kills Dick, sending him back to Purgatory, but it has the added side-effect of dragging Dean and Castiel along for the ride with Dick's soul.
After Dick is killed by Dean, Crowley appears to tell Sam that killing Dick has effectively defeated the Leviathans as they have only ever had one leader since the beginning of their existence and are now left directionless. Crowley takes Kevin captive and sends "a small army" of demons into SucroCorp to deal with the Leviathans left over in the building now that their leader is dead.
After the death of Dick Roman, the Leviathans lose all cohesion and cease to be a threat. By a year later, even the effects of their additives have disappeared, negating everything they had tried to do. However, not all of the Leviathans are gone after their defeat as they are briefly considered a suspect for a series of murders over a year and a half after their defeat before it is determined they are dealing with a bastard offshoot of djinn.
After killing Dick Roman, Dean and Castiel are transported to Purgatory with his soul. There, Dean is trapped for a year before escaping with the help of the vampire Benny. Castiel is eventually rescued by angels under the command of Naomi.
- ↑ 1.0 1.1 Meet the New Boss
- ↑ Swan Song
- ↑ The Man Who Would Be King
- ↑ The Man Who Knew Too Much
- ↑ 5.0 5.1 Hello, Cruel World
- ↑ 6.0 6.1 6.2 6.3 The Girl Next Door
- ↑ Shut Up, Dr. Phil
- ↑ Slash Fiction
- ↑ How To Win Friends And Influence Monsters
- ↑ Death's Door
- ↑ Party On, Garth
- ↑ Adventures in Babysitting
- ↑ Out With The Old
- ↑ Of Grave Importance
- ↑ Reading Is Fundamental
- ↑ There Will Be Blood
- ↑ 17.0 17.1 17.2 Survival of the Fittest
- ↑ 18.0 18.1 We Need To Talk About Kevin
- ↑ Pac-Man Fever
- ↑ A Little Slice of Kevin