Many are the good men who can resist murder, theft, and cruelty. But a touch of greed? A bit of laziness? These are the seeds of the ruination that can bring down the best of men!
Mephisto, sometimes using the name Mephistopheles or even Satan (among many others), is a powerful demonic shape-shifting supervillain from the Marvel comics as one of the main villains in the Marvel Universe. He is one of several such demons that feed off humanity's belief in The Devil so as to masquerade as Satan himself. In reality, however, Mephisto's origin seems to lie with the primordial Elder-Gods that ruled earth before being banished by Atum the God-Eater, the exact nature of this origin varies with story to story but tends to vary between the old gods becoming corrupt or the demons being formed by the already plentiful corruption found in the Elder-Gods. He is Ghost Rider and Silver's infamous archenemy, while serving as an enemy to other heroes like Spider-Man and Doctor Strange. He served as the main antagonist of the Ghost Rider series,a major villain in the silver surfer,Doctor Strange,and the avengers.
At any rate, Mephisto now rules over his own dark dimension, commonly called Hell but not related to the Biblical hell (though to the average human being it may as well be as it is equally as horrific), within this realm Mephisto rules supreme with only demons such as Blackheart (his own son) being capable of challenging him there.
Outside his realm, however, Mephisto becomes much more restrained, although still a virtually limitless sorcerer. He is aware of these limits and seeks ways to expand his influence throughout time/space but also, like many demons, enjoys causing misery and deception for no apparent reason other than malice.
Mephisto's main enemies are the Silver Surfer, Fantastic Four, Dr. Strange, and Ghost-Rider, Ghost-Rider is especially prominent since he was formed due to a pact with Mephisto but dedicated himself to stopping the devil rather than working as his servant.
Mephisto is also an enemy of Doctor Doom due to the demon having trapped and tormented the soul of his mother, Cynthia Von Doom (note that this is only relevant to the comic canon and may or may not apply to other versions of Dr. Doom).
Mephisto is often seen as the most powerful of all demons in Marvel cosmology, however he is officially of a "Hell Lord" status and thus is on par with beings such as Satannish or Marduk Kurios - basically this is a title given to a demon that is seen to exhibit so much power and malevolence that they are often mistaken as the Devil to mortals.
Mephisto is weaker than entities such as Beyonder but has been able to face Galactus and even Eternity on occasion. He has also admitted that he is weaker than The One Below All (who was revealed in Immortal Hulk).