Mephisto is an extra-dimensional demon whose origin is unknown. He rules a fiery pocket dimension that he calls "Hell" or "Hades" although it is neither the hell of the Christian religion nor the Hades ruled by Pluto, the Olympian god of the dead. Mephisto calls his extra-dimensional realm "hell" in order to exploit Earth human beings' belief in a single being of absolute evil, who is often referred to as Satan, who rules such a realm.
Mephisto resembles the traditional visual conception of the devil. (It is not known whether this is Mephisto's true appearance, or one that he has adopted in order to resemble the devil). He also allows himself to be called names that human beings give to their conceptions of devils, such as Mephisto, a shortened form of Mephistopheles, the name given to the devil in the Faust legends. Indeed, Mephisto has allowed people to believe him to be Satan himself. However, Mephisto is not the Biblical Satan, nor is he the actual devil such as the one depicted by Judaism and Christianity.