2. River Song
BBCHello, Sweetie. Much like Rose Tyler, fandom splits on the subject of River Song. Some love her, others think she's the worst thing to ever happen to the show. What isn't up for debate however is that having a character who's living their life in the reverse order from the regular characters is an incredibly difficult thing to pull off. Indeed, it's hard to think of another show that would even try. And yet Doctor Who not only attempted it in the character of River Song, it carried on pulling it off. It would have been forgivable, after Forest of the Dead, for viewers to assume that we just weren't ever going to mention Professor Song again. It would have simply been an interesting concept that the show had thrown out there and moved on from, not unlike Jenny, The Doctor's Daughter. But the show didn't move on from it (which is ironically what bothers a portion of fandom.) We came back to River time and again, and each time we saw clearly how the Doctor knew her more (just as we did) and she knew him less. By the time she confesses to Rory that she knows one day she'll look into The Doctor's eyes and he won't know who she is, we completely understand how that will feel to her. And then we remember that we've already seen that moment years earlier. The ultimate testament to how well River's introductory story works is how coherently her story hangs together if you watch all of the stories in the sequence River experiences them. If you haven't tried watching them in that order you should go do that right now. But not before reading about...