Four Horsemen of the Apocalypse

Four Horsemen of the Apocalypse, or Riders, are neither Angel nor demon, but natures/natural phenomenons, each having a separate conscience.

They manifest visually (human, thus can be damaged like humans with Ruby's Knife) during the Apocalypse, after having been personally instigated (except for Death, who had to be freed via a ritual) by Lucifer's release. But they were very much present before Lucifer's release. They are respectively known as: War, Famine, Pestilence, and Death. The Horsemen are neither angels nor demons, but rather a separate kind of being that cannot be destroyed.

Each has a special ring that channels their essential allotted power, without which they are hindered. However, Death is reasonably okay without it, his powers aren't reduced (his teleporpation, etc). Also, they each travel in a car (colored to resemble their steed's color in lore), in having gotten "with the times".

The Horsemen aren't on either side, Heaven or Hell, but rather they are ultimately loyal to one another and the jobs for which they were created. After Lucifer rises from his cage in Hell, he takes command of the Horsemen (seemingly through the use of a binding spell to compel them to comply with his orders) and directs them in enacting his genocide against humanity. It is revealed, however, that at least some of the Horsemen resent Lucifer's use of them in his fight with God, ultimately revealing that he only has limited control over them. Their rings, unknown to all but a few select individuals, are the keys to Lucifer's Cage in Hell, and thus the Horsemen collectively hold the key to sending him back.

Powers and Abilities
The Four Horsemen are amongst the most powerful beings in existence, more powerful than any monster, Ghost, Demon or Pagan Deity and even more powerful than most angels. However they require their rings to direct their powers (although Death's reasonably okay without it).

Collective Powers

 * Indestructibility - The horsemen cannot be destroyed, so long as their respective attributes exist.
 * Immortality - The horsemen exist so long as their respective attributes (War, Famine, Pestilence, and Death) exist.
 * Invisibility - The horsemen are naturally invisible, unless they choose to take form.
 * Manifestation - The horsemen can appear in human, corporeal form.
 * Shapeshifting - While in corporeal form, they could alter their appearance at will.
 * Superhuman Stamina - The horsemen never tire, literally (as they, as phenomenons, don't experience fatigue), and do not require food, water, sleep, or oxygen to sustain themselves.
 * Telekinesis - The horsemen can manipulate physical matter through power of will.
 * Teleportation - The horsemen can travel from place to place instantly, without occupying the space in between.

War

 * Illusion Casting - War could create illusions and hallucinations, which drove people to violence.
 * Superhuman Strength - War can exert more physical force than humans.
 * Telepathy - War can read the thoughts of other beings.

Famine

 * Demonic Exorcism - Famine could forcibly remove a demon from its vessel.
 * Gluttony Augmentation - Famine could enhance the sense of hunger in other beings, causing them to seek whatever it is they crave most until it resulted in their destruction.
 * Insatiable Hunger - As the embodiment of hunger, he constantly craved sustenance. This gave him the ability to devour anything - even the essences of demons and human souls.
 * Soul Reading - Famine can determine the state of a soul.
 * Telepathy - Famine was able to enter Dean's unconscious, telling him he was "empty inside."

Pestilence

 * Biokinesis - Pestilence can create, manipulate, and control diseases. He can also cause instantaneous illness in another being.

Death

 * Necrogenesis - He can cause instant death in anyone or anything. He once caused a man to collapse after simply brushing shoulders with him.
 * Nigh-Omniscience - Death has an awareness of the universe that exceeds that of the archangels, and is only rivaled by God.
 * Reality Warping - Death has nearly unlimited power. He was even able to alter the cosmos to cause an eclipse.
 * Resurrection - Death can bring any being he chooses back to life. He even retrieved Sam's soul from Lucifer's cage, without being hindered by either Michael or Lucifer, or the supernatural barriers strong enough to keep 2 Archangels locked inside. He could even bring multiple people back to life just with his passing. It's interesting to note that, unlike other beings with resurrection, he seemed to have some control over how they came back - when he brought back a town-full of people, he made sure that they would eventually turn into killers, under Lucifer's orders.
 * Weather Manipulation - It is heavily implied that Death is responsible for the Great Flood of Genesis 6. He was also going to wipe out Chicago with a massive storm when Dean found him.

The Horsemen
"I'm waiting to hook up with my siblings; I've got...three. We're gonna have so much fun together."

- The Horseman War

They are powerful beings.

Previously just in their "day jobs", without physical form, when Lucifer rises, everything gets started, the Horsemen get out of their "day jobs" (as Anna refers to it), and become more active, serving Lucifer seemingly through an enchantment, most notably with Death.

Their, or at least War's, life before the breaking of The 66 Seals was all over the place, in a multiple existence manner.

Now that Lucifer is free, they have begun to up the stakes and spread their powers across the Earth to turn it into Hell, which sticks with Cas' comment, "If Lucifer rises, Hell rises with him".

In Death Takes a Holiday Alastair remarks the Horsemen are well aware of Lilith's plans and are "jonesing for the Apocalypse".

Unlike regular Demons or higher-tier Demons like the Seven Deadly Sins and white-eyed demons, the Horsemen are virtually indestructible. The only way to destroy them would be to annihilate all war, famine, pestilence and death in the world, though in The Devil You Know it is revealed that separation from their rings leaves them in a withered, near-catatonic state.

The Horsemen have a very slanted view of humanity and see themselves as just bringing out in humanity what is already there. Both War and Famine have said humans "only need a little push" in order to do horrible things, and both have surprisingly shown a level of disgust and contempt toward how easily corruptible humans are and what they can do. Pestilence prefers diseases to people, claiming that belief of disease being a bad thing is just because of sick people, and he can never understand why God has such love for humanity.

It is unknown if their human forms are constructions, illusions, or actual human vessels; Anna hinted that they may be using vessels when telling Castiel "The Horsemen can go back to their day jobs" once the Apocalypse has stopped. Another hint to what they actually are is in Good God, Y'all, where War states that the person he is imitating is really dead and buried in a ditch, which suggests that they do not require an actual human vessel, and that they can become whomever they wish; more like a changeling, they can imitate or construct an appearance of whatever they choose.

Each Horsemen also possesses a ring that allows them to channel and focus their power, and, while it doesn't kill them, separating them from their rings is the only known way to drive them off. In Hammer of the Gods Gabriel reveals the rings are actually the keys to Lucifer's Cage and if the brothers can collect all of them and trick Lucifer back into the cage, they can be used to reopen and close it.

In Two Minutes to Midnight it is shown that the Horsemen cannot be properly filmed, as when Dean and Sam are watching a camera for Pestilence, they find him because his face and ring are hidden with a static-like distortion.

It also hinted that Lucifer may not have total control of the Horsemen as it is revealed in The Devil You Know that Dean and Sam are instructed to find Death and Pestilence's handlers in order to acquire their rings. Lucifer states in Abandon All Hope... that the Horsemen (Death in this case) are very demanding and require certain rituals and agreements to stay happy and compliant. Their handlers are revealed in The Devil You Know to be more like personal attendants seeing to each Horseman's personal needs and overseeing some of their interests. Brady, for example, has been overseeing Pestilence's Croatoan Virus trials while the Horseman himself has been setting the stage for the virus's release.

The Horsemen also have a very deep loyalty to one another that supercedes any allegiance to Lucifer. For example, Pestilence wanted to kill the brothers in revenge for what they did to War and Famine. When a minion warned him they were under orders not to harm the brothers, Pestilence raised his voice to a Demonic level and stated if the Devil wanted them so badly he could glue them back together after.

War
Appearing in Good God, Y'all, War arrives in Rufus' town in the guise of a well-known resident whom he killed a few nights before. In the Bible, he is said to ride a red horse but these days he "got with the times" and travels in a red sports car (a mustang fastback from the late 60's to earlier 70's model). Once in town, he destroys the town's only exit and then gets to work on the townspeople by using his ring to generate hallucinations, making the people believe that others around them have been possessed by demons. War hates acting directly because in his opinion the best way to cause chaos is to induce panic and let humans take care of the rest. Realizing that they cannot kill War (as the only way to do so is to eliminate all war in the world), the Winchesters instead cut off his ring finger, breaking the spell he cast over the town and forcing him to depart. In The Devil You Know, Brady reveals that the Winchesters have reduced War and Famine to near catatonic states. War's ring is gold, does not have a stone, and appears to be a wedding ring.

Famine
Famine appears in My Bloody Valentine as a sickly old man. Improvements in farming and agriculture have severely weakened Famine, resulting in his current state. Because of this, Famine can barely infect anyone by himself, forcing Lucifer to send lower level-demons to care for him until his powers are fully regenerated. Despite his weakened state, he is still strong enough to resist an assault from a Demon-blood juiced Sam, and explains all the Horsemen are immune to Sam's powers. Like his brother War, he too possesses a ring that allows him to focus and direct his powers. His ring is silver with a black stone.

Pestilence
Pestilence first appears at the end of Hammer of the Gods, buying flu medicine (which he doesn't need, as he is sickness) from a small drugstore and spread some disgusting mucus over everything. He drives a sickly green/white car with a license plate that spells "sick and tired". He is accompanied by a swarm of flies and has the appearance of a man suffering a heavy cold, though this appears to be a ruse since, after leaving the drugstore, he straightens up and laughs while throwing the medicine away. His ring is gold with a pale green stone.

Death
Death doesn't make a physical appearance in Abandon All Hope..., but his presence is released from his prison by Lucifer's ritual. Although again not seen on-screen, Death causes the dead to rise from the grave in Dead Men Don't Wear Plaid. He makes his first visible appearance in Two Minutes to Midnight, arriving in Chicago. After getting out of his white car, he walks down the sidewalk, where a man on his cell phone rudely bumps into him and collapses dead soon thereafter. Crowley later helps Dean track Death to a pizzeria, where Death makes a deal with Dean to give him his ring in exchange for him do all in his power to put Lucifer back into his cell. His ring is silver with a white stone.

Death is the eldest of the Horsemen and is older than most creatures can understand; he explains to Dean that the entire galaxy is still "in its diapers" in comparison to him. In a conversation with Dean he claims to know God by stating that neither entity can remember their true ages anymore. Death's Sickle reacts in the same way as Dean's pendant reacts to God—glowing hot in his presence. Due to his age Death is very detatched from the rest of the world and does not really care that much for the Apocalypse and those involved, thinking them to be little more than bacteria. Dean, who is an important tool for the war, is highly insignificant to Death in the grand scheme of the universe, and he (like Pestilence) openly despises Lucifer, who has him under his control through the use of a binding spell. In a similar manner to Gabriel, Death compares Lucifer to a spoiled, bratty child throwing a tantrum, and despises the fact he is using Death as a weapon.

Family

 * Each other (Kindred)

Season 5

 * Good God, Y'all
 * My Bloody Valentine
 * Hammer of the Gods
 * Two Minutes to Midnight

Season 6

 * Appointment In Samarra

Season 7

 * Meet The New Boss