Taken from Wikipedia:
Mephistopheles (/ˌmɛfɪˈstɒfɪˌliːz/, German pronunciation: [mefɪˈstɔfɛlɛs]; also Mephistophilus, Mephistophilis, Mephostopheles, Mephisto, Mephastophilis, and other variants) is a demon featured in German folklore. He originally appeared in literature as the demon in the Faust legend, and he has since appeared in other works as a stock character.
The name Mephistopheles is associated with the Faust legend of a scholar, based on the historical Johann Georg Faust. In the legend, Faust wagers his soul with Mephistopheles.
The name appears in the late 16th century Faust chapbooks. In the 1725 version, which Goethe read, Mephostophiles is a devil in the form of a greyfriar summoned by Faust in a wood outside Wittenberg. From the chapbooks, the name entered Faustian literature. Many authors have used it, from Christopher Marlowe to Goethe. In the 1616 edition of The Tragical History of Doctor Faustus, Mephostophiles became Mephistophilis. Mephistopheles in later treatments of the Faust material frequently figures as a title character: in Meyer Lutz’ Mephistopheles, or Faust and Marguerite (1855), Arrigo Boito’s Mefistofele (1868), Klaus Mann’s Mephisto, and Franz Liszt’s Mephisto Waltzes.