The "devil" actually looks like Moses with the Ten Commandments. I don't remember the exact specifics as to why, but appearently at some point somebody somewhere was translating the Bible and screwed up. Appearently somewhere in the Old Testament it says that Moses had rays of light coming out of his head. The genius who was translating the that passage mistranslated the word for "rays" as "horns", and because of that mistranslation, there were many images of Moses created for a long time afterwards wearing horns on his head and looking rather satanic.
(Art History education talking here....)
