Who's your favorite back-stabbing anti-hero?

We love anti-heroes in general, from Han Solo to Bronn. But the most exciting anti-heroes are the ones who can't be trusted. At all. The ones who will turn on their friends if someone offers the slightest incentive. The betrayers. Who's your favorite totally untrustworthy good guy? (Or gal?)

As usual, please include a photo of your favorite untrustworthy ally, so we can admire his or her cunning. Or if they're from a book, a book cover will work great.