Matthew Abbadon from Lost. You kind of have to know the show to see why, but truly one of the most bizarre and mysterious characters ever created. Still don't fully understand what his purpose was.
I watched LOST religiously when it was on TV. I remember Abbadon well. He was an odd fellow, though I found Richard Alpert (before his flashback episode) to be the most mysterious character, followed by the nameless man in black.
Benedict Arnold 