3. River Song
River Song was a game-changer for the 11th Doctor. We all know that her story is awesome, but her character is excellent too. She's headstrong, independent, and cleverand just look at that hair! Don't like how she bosses the Doctor around? Well, neither does he, but he still loves her (interpret the word "love" as you will), and that's the brilliant thing. Sure, her superiority complex and cocky attitude can be grating at times (at other times, of course, it's seriously badass), but she's still a marvelous character. She's multi-factedsometimes, she seems like a manipulative megalomaniac; other times, she is selfless and sensitive; other times, she is a dangerously focused killing machine. You certainly cannot pin down River Song, even in retrospective analysis. She was an enigma from the startand that's brilliant.