Belphegor

"Look, I-I'm not some Crossroad Demon. I'm not even one of those black-eyed goons who crawled his way up here to eat, you know virgins and puppies and, uh, virgin puppies. Look, Downstairs I punch a clock. A soul comes in, I torment it, it's what I do. (…) The point is, I like my job. I like Hell the way it is -- or -- or was. So, all those bad guys? You want them back where they came from, right? Well, me too."

- Belphegor introducing himself to the Winchesters and Castiel.

Belphegor is a demon who worked as a torturer in Hell and becomes an ally of the Winchesters after God begins the end of the world.

Background
When Belphegor was human, his people were worshipping a giant rock that looked like a penis and the people were ugly with a lot of humps.

During his time in Hell, Belphegor becomes a torturer of souls, never once going to Earth. During Dean Winchester's time in Hell, Belphegor witnesses Dean torturing souls with Alastair and becomes a fan of his work.

When God begins the end of the world, he opens every door in Hell, allowing all of the souls to escape. Belphegor uses the opportunity to leave Hell for the first time since he died as a human.

Season 15
In Back and to the Future, after escaping from Hell, Belphegor possesses Jack Kline's corpse. At first the Winchesters think that Jack has come back to life, but Castiel is able to tell that it's actually a demon using Jack as a vessel. Belphegor explains that he just arrived and needed a body, commenting that he would show them his eyes if Jack's weren't burned out. Putting on a pair of sunglasses to blend in, Belphegor introduces himself and ignores Castiel's orders to get out of Jack's body. Castiel pins Belphegor to a wall and demands that he get out of Jack with an angel blade to his throat, but Belphegor insists that he can help. Castiel continues to threaten Belphegor, calling him an abomination, causing Belphegor to mock Castiel's trench coat. Dean finally pulls Castiel off of the demon so they can hear him out as they need the help. Castiel is angry as Belphegor is defiling Jack's corpse, but Dean states that Jack's gone and if Belphegor can help they should let him which Sam agrees to.

Sam tries to introduce them to Belphegor who reveals that he already knows who they are as he reads the papers. Belphegor guesses the whole hellmouth thing is them and is shocked when Castiel explains that it was actually God. Belphegor explains his role in Hell and that he likes his job and his role in Hell as it was. As a result, he also wants all of the souls back in Hell. Belphegor admits that he can't fix the whole situation, but he can get them out of their current danger. Gathering graveyard dirt and Castiel's blood, Belphegor slaps his hands together and casts a spell that causes the zombies to stop. Emerging from the crypt, the group finds the zombies lifeless on the ground and Belphegor explains that he simply blasted the souls out of their bodies, leaving Dean wondering where the ghosts are.

Belphegor joins the Winchesters and Castiel in the Impala, admiring his vessel in the mirror and commenting "for now" when Dean thinks they are only dealing with a ghostpocalypse confined to the one area. Belphegor points out that all of the souls have to go somewhere and when Sam asks how many souls they are dealing with, Belphegor states that there are two to three billion souls in Hell. Dean states that they should go back to the Men of Letters bunker and find a way to close the rift unless Belphegor has a better plan. Although he admits that he doesn't have a better plan, Belphegor suggests that they buy some time by containing the ghosts with a spell that will create a barrier a mile wide which no ghosts can enter or leave. Castiel realizes that Harlan, Kansas is less than a mile from the cemetery and thus within range of the barrier. As a result, Dean suggests that they evacuate the town by lying. After the Winchesters spot a car by the side of the road covered in blood, Belphegor remains in the car with Castiel while they investigate.

The next morning, as Sam begins the evacuation of the town, Dean orders Castiel to help Belphegor to get the ingredients for the spell while the Winchesters handle the evacuation. Castiel, unable to even look at Belphegor, instead leaves to help Sam with the evacuation while Dean helps with the spell. Dean ignores Belphegor's interest in the Equalizer and Belphegor expresses interest in the way people look in the present, commenting on how different people are now to when he was last on Earth when Belphegor was human, annoying Dean. Dean questions when Belphegor will get out of Jack's body and he promises to when he finds another vessel, commenting that he didn't take one at the cemetery as the bodies there were all too "wormy" for him and difficult to blend in. Dean admits that Jack was their kid "kind of," causing Belphegor to apologize. At Dean's prompting, Belphegor tells him that they will need a big bag of salt for the spell and a human heart.

When Dean returns with a bag of rock salt, Belphegor tells Dean that he is a fan of Dean, having witnessed Dean at work in Hell with Alastair which Dean brushes off as being a long time ago. Dean questions Belphegor on the current state of Hell and he explains that every door in Hell sprang open all at once, causing Dean to realize that this includes Lucifer's Cage. Concerned, Dean asks about Michael and Belphegor tells him that last he heard, Michael was just sitting in the Cage, but suggests that if Michael got out, he will want revenge.

Walking together, Belphegor brings up their need for a human heart for the spell and Dean states that he is planning to hit the local morgue. However, Belphegor states that they need a fresh heart. Investigating a scream, the two find the local sheriff dead and Belphegor rips out his heart to use in the spell. With Dean's breath becoming visible, he tells Belphegor they need to move before he is attacked by Constance Welch. With the ghost turning on him, Belphegor claims not to know Dean and tries to talk her down only to have Constance slash his hand open. Dean dissipates the ghost with an iron bar and orders Belphegor to perform the spell immediately. Placing the heart in a pile of salt, Belphegor casts the spell, trapping the ghosts within a one-mile radius of the cemetery and containing them for the time being.

After trapping the ghosts, the Winchesters, Castiel and Belphegor bring a mother and daughter Sam and Castiel rescued to the high school where the town's residents are gathering. Belphegor makes a sarcastic comment as the Winchesters tell the two residents not to tell anyone about the ghosts or angel as it might freak them out. Noticing the awkwardness of the situation with Dean and Castiel, Belphegor asks if Castiel wants to talk about it, but he just ignores the demon.

Personality
Belphegor displays a generally friendly and sarcastic demeanor, using the phrase "you know" a lot in conversation. He also appears to be somewhat pessimistic, stating that his spell only got the ghosts out of the bodies they were possessing for now and saying the same thing when the Winchesters comment that the ghostpocalypse appears to be confined to their immediate area. When Dean brings up finding a way to close the rift to Hell, he expresses pessimism on whether or not they actually can. His behavior tends to be obnoxious and annoying to those around him at times.

Despite his friendly demeanor, Belphegor has a sadistic side as shown by his enjoyment of torturing souls in Hell. He is a fan of Dean's, having seen Dean torturing souls in Hell with Alastair, calling Dean's work "art."

Belphegor appears to be something of a coward when faced with a situation out of his control. When threatened by Castiel, he replied with snark, but knew that the Winchesters and Castiel needed his help more than they wanted to kill him. However, when faced with the ghost of Constance Welch, Belphegor attempted to lie and talk his way out of trouble rather than defending himself in any way against the ghost.

Powers and Abilities
Belphegor appears to be a regular demon with all the powers of one.
 * Demonic Possession - As a demon, he requires a vessel to walk the Earth.
 * Immortality - As a demon, he was immortal unless killed. Belphegor mentioned that when he was human, people were worshipping a rock that looks like a penis though it is unclear how long he has been a demon. Belphegor only states that "it was awhile ago" that he was human.
 * Invulnerability - As a demon, he is invulnerable to all forms of conventional harm.
 * Super Strength - As a demon, he is stronger than most humans and monsters. Belphegor was able to punch his bare hand into a dead body to rip out the man's heart.
 * Spell Casting - Belphegor displays an impressive knowledge of magic, being able to cast spells to cast souls out of the bodies they are possessing and to set up a barrier to trap ghosts.

Weaknesses
Belphegor presumably possesses all of the regular weaknesses of a demon.
 * Seraphim - Belphegor appeared to be wary of Castiel when threatened by him and was easily pinned against a wall by him.
 * Angel Blades - As a regular demon, he could be killed with an angel blade and was wary of one when Castiel threatened him.

Appearances

 * Season 15
 * Back and to the Future
 * Raising Hell

Trivia

 * As Jack's eyes are burned out, its unclear what color Belphegor's eyes are. Belphegor himself comments that he'd show his eyes if he could but Jack's lack of eyes prevents that. However, he has stated that he is neither a black-eyed demon nor a crossroad demon.
 * Despite his vessel having no eyes, Belphegor's interactions with the world around him suggest that the demon can see just fine without them. This is contrary to the Waitress demon in Lazarus Rising who was blinded when her vessel's eyes were burned out by Castiel. However, in her case, the demon was possessing the vessel at the time it suffered the injury rather than taking over the body afterwards.
 * Belphegor suggests that the Winchesters and Castiel are responsible for the "hellmouth" situation. In Buffy the Vampire Slayer, hellmouth is place in which dimensional barriers are particularly weak, allowing to relatively easily move between dimensions in such places. Thus, a hellmouth is practically a gateway between different dimensions. Specifically, the town Buffy lives in, Sunnydale, is built just a top a rather dangerous hellmouth, connecting earth with an awful hellish dimension, thus Buffy must prevent from being opened. A second hellmouth is revealed to exist in Cleveland, Ohio in the Buffy series finale.
 * In The Gatekeeper Trilogy of the Buffy the Vampire Slayer novel series, Belphegor is one of the Big Bads.