So Many Satans!
“Satan” has become a name of its own, but originally, it was more of a title for an adversary of some sort, even a human one. So the idea of there being several satans is biblically sound. But as demons moved into the Middle Ages, there tended to be one supreme lord of hell. Sometimes the name changed based on the artistic sensibilities of an author (the creation of Apollyon may fit here). Sometimes there was an actual regime change (as when Satan lost control of hell to Beelzebub). Sometimes some particular image of Satan takes centers stage (the fictional creation Mephistopheles from Faust becoming synonymous with the king of hell).
Demons have very fluid identities, but this is particularly the case with demons who have been promoted to “King of Hell.” Beelzebub and Mephistopheles, for example, are unique spirits: the story in which Beelzebub becomes the regent of Hell has him arguing with Satan as a separate character. But it seems that the spirits in this category become aspects of each other: Samael, Lucifer, Azazel all tempted Eve in the garden of Eden. Lucifer’s name is nearly synonymous with Satan’s name. Lucifer, Satan, Azazel are all the serpent that will be cast into the inferno at the end of the world. Once a spirit becomes a satan, it seems that they also become Satan, losing themselves in the myth of that figure.
Anyway, below please find a list of the the reigning king(s) of hell, at least from a particular window of time.