A demon frequent in occult mythology, and a cheif member in the Faust legend. Often seen in the form of a dog, horse, or raven familar.
Mephistopheles promised to serve as Faust's servant for 24 years.
A name for a demon of devil associated in the Faust legend.
By the 17th century, the name had begun to lead an existence independent of the Faust legend.
Now it is just another word smart people can call people they don't like. Since is it fairly unknown, it's handy because people won't argue with you for fear of looking stupid by asking what it means.
"President Bush... jeez, what an evil mephistopheles."