Princes of Hell

The Princes of Hell are the first generation of demons created by Lucifer himself after the creation of Lilith. They were originally generals of his demonic armies, but have since become separated from Hell, opting instead to hide out on Earth. The one known exception to this was Azazel, who remained loyal to Lucifer until his death. After a promise to rule at Lucifer's side, Dagon briefly served him once more as the protector of Lucifer's son. Following the deaths of Azazel, Ramiel and Dagon, Asmodeus is the only remaining Prince of Hell.

History
After creating the first demon, Lilith, Lucifer created the four Princes of Hell as the first generation of demons aside from Lilith. These demons were Lucifer's rightful successors to the throne of Hell and acted as demonic generals. Eventually, three of the Princes, Ramiel, Asmodeus and Dagon lost interest in Lucifer's plans and left Hell to live peacefully on Earth. These Princes of Hell were believed to have been killed afterwards by even the angels, but the demons simply allowed everyone to believe so.

However, Azazel remained fanatically devoted to Lucifer and became the Ruler of Hell, setting out to find a way to release Lucifer and begin the Apocalypse. In 1972, Azazel was able to contact Lucifer in his cage from St. Mary's Convent and was given instructions to release Lilith from Hell to find a very special child to act as Lucifer's vessel. Azazel went on to make a series of deals that would allow him to enter the homes of couples with six month old children in ten years time. At the time of fulfilling the deals, Azazel killed several of the mothers if they interrupted him, including Mary Winchester. This set her husband John and his sons Sam and Dean on a path of vengeance. With the help of Jake Talley, Azazel succeeded in releasing Lilith, but was killed by Dean with the Colt. As a testament to his strategic mind as a general of hell's army, Azazel and his master plan, despite his death, was a success; Azazel's ritual prepared Sam's body as Lucifer's vessel, Lilith then broke the seals on Lucifer's cage, freeing the fallen archangel, and thus started the Apocalypse which almost succeeded.

In 2010, following the defeat of Lucifer, the King of the Crossroads Crowley approached Ramiel to take rule of Hell as was his rightful place with Lucifer locked away and Lilith and Azazel dead. However, Ramiel refused, stating that Azazel had been a fanatic but the other Princes had lost interest in Lucifer's plans long ago and simply wished to be left alone. Before leaving, Crowley left the Lance of Michael and the Colt with Ramiel.

In 2017, a resurrected Mary Winchester was sent by the British Men of Letters to steal the Colt from Ramiel. The attempt left Wally dead and the Seraph Castiel mortally wounded. Ramiel was eventually killed by Sam Winchester with the Lance of Michael and Castiel was saved, but Ramiel warned that his sister, Dagon, had taken an interest in Lucifer's son. Indeed, Dagon later saved the pregnant Kelly Kline from two angel assassins sent to track her down and kill her. Under promise of ruling at Lucifer's side if she protected his son, Dagon served as Kelly's protector from both angels and hunters and was granted new powers as a result.

With less than a month left before Lucifer's child is born, he briefly empowers Castiel and gives him the power to kill Dagon, leaving Asmodeus as the only surviving Prince of Hell.

Powers and Abilities
As some of the first demons ever created, the Princes of Hell are arguably the most powerful demons to ever live. The three Princes of Hell encountered by the Winchesters display many powerful and sometimes rare abilities.
 * Demonic Possession - As demons, the Princes of Hell require a vessel to walk the Earth.
 * Super strength - Azazel enhanced his host's physical strength to a superhuman level, to an even greater extent than most other demons do. Azazel was able to casually snap John's neck and could overpower humans, demons, and even ghosts. Ramiel was strong enough to throw around Crowley, a powerful demon in his own right and easily defeat Castiel, a weakened Seraph.
 * Advanced Telekinesis - Azazel could move people and objects using only his mind. He was very skilled with this ability, able to use it on multiple targets at once, restraining them so they couldn't even cry out for help, and throwing grown men considerable distances, by flicking his wrist. He was able to keep Mary pinned to the ceiling, without even being in the room. Dagon was similarly able to fling around several hunters effortlessly.
 * Biokinesis - Azazel demonstrated the ability to psychically injure humans, even inducing fatal internal bleeding with a mere glare. One of the omens of Azazel's arrival also included mass cattle deaths.
 * Pyrokinesis - Azazel could generate and manipulate fire. His power over fire was extensive enough that he could render entire buildings ablaze in minutes or even seconds.
 * Immunity - Azazel was immune to several demonic weaknesses: he was immune to holy water, salt and was able to walk on holy ground. Ramiel was immune to devil's trap bullets.
 * Invulnerability - Princes of Hell cannot be harmed by normal means. The only weapons known to be able to kill them are the Colt, the First Blade, Death's Scythe and the Lance of Michael. Ramiel was immune to demon killing knife and angel blades, however the knife caused him a slight amount of pain. When Dagon was shot several times, she was not only unharmed, but it appeared to cause her no pain. Castiel states that Dagon is extremely hard to kill at one point.
 * Immortality - The Princes of Hell are some of the oldest demons to exist, having lived for many millennia.
 * Resurrection (by deals) - Azazel was able to resurrect dying or dead humans, though he had to first make a deal with a living human, he explicitly stated that he couldn't resurrect people unless a deal was made, dismissing it as "red tape".
 * Super Stamina - Azazel did not require food, water, oxygen, or sleep to sustain himself.
 * Reality Warping (by deals) - Azazel could alter the world around him in the context of a demonic deal. Unlike all other demons, he did not require a soul to power the deals he made. However, he still had to obey the rules of the demonic soul deals. As he said in reference to Sam's resurrection at the end of Season 2, "You see, demons can't resurrect people unless a deal is made. I know, red tape--it'll make you nuts."
 * Teleportation - Azazel could travel instantly from one place to another including Hell and Earth without occupying the space in between, he was quick enough to use this to avoid bullets. He was able to move fast enough to kidnap Sam and remove him in seconds. Dagon was able to use this ability to quickly dodge attacks, using it in a similar manner to super speed.
 * Dream Walking - Azazel could enter others' dreams, he used this ability to enter the dreams of his special children when they were asleep in "All Hell Breaks Loose - Part 1" and "All Hell Breaks Loose - Part 2". He was mentioned as having done so in "Simon Said" and "Hunted".
 * Weather Manipulation - As great masses of demons can, Azazel's presence alone could cause thunderstorms, massive temperature fluctuations, and sudden gusts of wind. When Dagon teleported to where the Winchesters were with Mick Davies and Renny Rawlings, her mere travel caused high gusts of wind and lightning strikes.
 * Healing (by deals) - Azazel restored a comatose, dying Dean to full health in "In My Time of Dying" and repaired John's broken neck in "In the Beginning" though in both cases he had to make a deal to do so.
 * Electrokinesis - Azazel's mere presence caused lights to flicker, electronic devices to go haywire, and clocks to stop. He could also do this at his will.
 * Memory Manipulation - Azazel could erase memories as seen when he erased Dean's memories of his near-death experience and John's memories of Azazel killing him.
 * Super senses - Azazel was able to tell Dean wasn't one of his special Children, simply by smelling his neck. Ramiel also could sense Castiel's "smell".
 * Flight - When in his disembodied smoke form, Azazel could fly.
 * Spell Casting - Azazel was able to perform a ritual, by sacrificing a group of nuns, which allowed Lucifer to speak to him while he was still in the Cage.
 * Mind Control - Dagon was able to compel Dr. Turner to tell Kelly Kline "everything is a-okay."
 * Thermokinesis - Dagon was able to heat up the Colt to the point that the barrel melted.

Weaknesses
Due to their sheer power, the Princes of Hell have very few known weaknesses.
 * Devil's Trap - A devil's trap was able to keep Azazel out, but devil's trap bullets had no effect on Ramiel. However, Ramiel was avoiding the trap set by the brothers.
 * Holy Fire (possibly) - It was used against Ramiel to trap him before he broke free by using Lance of Michael.
 * The Colt - This gun was able to kill one.
 * Lance of Michael - The Lance was able to kill one.
 * Nephilim - While empowering Castiel, Lucifer's son was able to give him the strength to easily overpower Dagon, render her powerless and burn her to ashes.

Known Princes of Hell

 * Azazel  (deceased)
 * Ramiel (deceased)
 * Dagon (deceased)
 * Asmodeus

Appearances

 * Season 1
 * Pilot (in silhouette)
 * Scarecrow (unseen, communicates with Meg)
 * Shadow (unseen, communicates with Meg)
 * Salvation (in silhouette)
 * Devil's Trap
 * Season 2
 * In My Time of Dying
 * Croatoan (unseen, communicates with Duane Tanner)
 * All Hell Breaks Loose - Part 1
 * All Hell Breaks Loose - Part 2
 * Season 4
 * In The Beginning
 * Lucifer Rising
 * Season 5
 * Dark Side of the Moon (as an illusion of Mary)
 * Swan Song (in flashbacks)
 * Season 6
 * Exile on Main Street (as Dean's hallucination)
 * Season 12
 * Stuck in the Middle (With You)
 * Family Feud
 * Somewhere Between Heaven and Hell  (video footage and mentioned)
 * The British Invasion
 * The Memory Remains (mentioned only)
 * The Future

Trivia

 * They can be seen as demonic counterparts to the four Archangels of Heaven.
 * As the son of the current King of Hell, Gavin MacLeod considered himself to be a Prince of Hell.
 * While they are called "Princes", Dagon is female. However, she is still specifically called "Dagon, Prince of Hell" by Castiel to the Winchesters when he warns them about her.
 * Of the three deceased Princes of Hell, two have been killed by one each of the Winchester brothers. Only Dagon of the three deceased Princes was not killed by a Winchester.
 * Before his death, Ramiel possessed both the weapon that killed his brother Azazel and the weapon that would ultimately kill him.
 * Although not revealed until the 12th season, Princes of Hell were the first demons to appear on the show, with Azazel appearing in the Pilot. They were also the first supernatural creature to appear as Azazel appears in the very first scene of the show.
 * In each case that a Prince of Hell was killed by a Winchester, it was done with the aid of one of their parents. In the case of Azazel, John Winchester distracted him long enough for Dean to get the Colt and shoot Azazel. In the case of Ramiel, Mary Winchester distracted him with an angel blade to the back, enabling Sam to grab the Lance of Michael and stab Ramiel.
 * In Supernatural: One Year Gone, Dean has to stop a plot to raise the Four Princes of Hell. In the non-canon novel the Princes are Lucifer, Belial, Leviathan and an unnamed fourth Prince.
 * In the The Satanic Bible by Anton LaVey, the "The Four Crown Princes of Hell" are Satan, Lucifer, Belial, and Leviathan.
 * In The Memory Remains, Sam discovers that the Men of Letters had very little on the Princes of Hell amongst their many books on demons and nothing useful.
 * Both Azazel and Dagon survived attempts on their lives with the Colt. While Azazel was eventually killed with the legendary gun, Dagon avoided all attempts to kill her with it and eventually destroyed the Colt.