Who's your favorite evil genius?S

Sure, the hero wins in the end — but we all secretly root for the villain. Especially if he or she is super, mega-genius smart. Who's the most awesome evil genius in all of science fiction and fantasy?

Please include a picture or clip of this maniacal polymath. And please mention the name of the story he/she comes from, along with why he/she is so cool. Thanks!

Top image: The Master from Doctor Who.