There have been many iterations of The Joker -- Batman's ultimate foe -- in film and television over the years, but none as iconic as Heath Ledger's fascinating, anarchic take on the role in Christopher Nolan's 'The Dark Knight.' Ledger took a darkly comical villain and really exploited the most evil, apathetic parts of him. Where Jack Nicholson and Cesar Romero played up the clownish flamboyancy of the character, Ledger must have really done his homework because this is the kind of Joker we'd only gotten to see in the comic books. The guy has no real motive outside of creating pure and utter chaos -- and what's scarier than a villain who has no motive and can't be reasoned with?