9. Chuck Bass - Gossip Girl
You can tell from Chuck's original treatment on Gossip Girl that he was never really supposed to be one of its protagonists. In the first few episodes (hell, most of the first season), he's this rapey, entitled douche who is sort of friends with Nate Archibald, but really just exists to make everyone else's life miserable. He tries to sexually assault Dan's little sister in one episode, and he's constantly blackmailing and generally annoying all of the various characters on the show. By all accounts, he's pretty much an antagonist, and the closest thing a show about rich kids on the Upper East Side has to a villain. But somehow, he's one of the most enduring characters on the show. Once he starts dating Blair, a lot of his rough edges start to soften, and he becomes a much more sympathetic character. In fact, you reach a point in the series where Nate and Serena, originally two of the show's biggest leads, start to take a backseat to the antics of Chuck and Blair. No one can match the deliciously amoral streak they bring to a relationship, especially compared to the dull, static characters that fill the rest of the show. Together or apart, they're the ones you can't stop watching.