Played By: Heath Ledger
Movie: The Dark Knight (2008)

What makes The Dark Knight's Joker so bone-chilling is not just his casual gun-slinging and throat-slitting. He's unpredictable. He's impenetrable. There's nothing about him that any feeling human can connect to. Hell, save for a quick mention of how he got his maniacal smile from his father, he doesn't even have much of a motive to be wreaking havoc on the citizens of Gotham. There are no records indicating that he exists. It's as if the Joker simply appeared. 

Undoubtedly, the character wouldn't have been so menacing had it not been for the Oscar-winning performance of the late Heath Ledger, who lived alone in a hotel room for a month, where he'd practice the Joker's maniacal mannerisms and even keep a diary recording the villain's thoughts and feelings. Some speculate that the emotional trauma Ledger put himself through took a toll on the actor, leading to his tragic, accidental death. —TA