Mephistopheles, aka Mephisto, is the demon best known from the Faust tale, wherein Faust sells his soul:
http://en.wikipedia.org/wiki/Faust
Mephisto is the master bargainer, the heart of the legends of Devils’ Bridges and Crossroads tales. He enjoys offering contracts (the majority of demons do not make bargains, but many mortals believe otherwise, so Mephisto has enough potential clientele to keep him permanently in business). His typical stipulation is that the client will have 6 years to enjoy whatever they’ve wished for, and then his debt…the client’s soul…is called in.
His usual form is a tall, slender humanoid, with handsome features. His skin is pearlescent grey, he sports long black hair and a goatee. Unlike many of the other Princes, he does wear clothes, and maintains his good-looking features, because as he explains to Belial, “he does have to work with the public”. It is said that his eyes are different to everyone who sees him.
azbaelus 