Martin Sheen as The Illusive Man

You know him as: President Bartlet (The West Wing), Capt. Willard (Apocalypse Now)

Martin Sheen made the Illusive Man one of the best morally ambiguous anti-tagonists we've ever seen. Yeah, we just made up the term "anti-tagonist". It means "someone so badass you can't even tell if he's an antagonist or a protagonist". Deal with it. His retreat from that gray area into full on bad guy in number three would have been disappointing if it hadn't been for his desperate belief that his course of action was the right one. And Sheen pulled it off perfectly.