So I've been thinking recently about who the best bad guy is, in any form of media. I think often the best parts of classic movies is the bad guy, not the hero, the best example being the Joker in the Dark Knight, but the older Bond films also come to mind (and IMO one of the failures of the modern Bond films is not having decent bad guys until Skyfall). Dr Evil, stupid stereotype though he is, is also probably the best part of the Austin Powers movies.
So I was wondering who you guys think is the best bad guy? In terms of how much they bring to their respective franchise, not how evil he or she may be.
IMO it's easily Darth Vader as the greatest villain. Everything about him oozes power and menace, even if he's not especially evil, he is simply so awe inspiring that simply his presence draws the viewer's attention.