River Song
While River Song was technically never a companion – instead meeting up with the Doctor for a series of adventures along the course of her lifetime and through several of his regenerations – it’s impossible to put together a list like this and not include her. One of the most controversial figures of modern day Doctor Who, it’s difficult not to have an opinion about her character and her timey-wimey, extremely nonlinear life story.
River is brash, brilliant, brave and utterly sure of herself at (almost) all times. An archaeologist, a professor, a wanted space criminal, a time traveler and seemingly everything in between, it’s easy to imagine her having a full, important life in between visits from the Doctor. She’s one of the few people who isn’t intimidated by the Time Lord’s vast power, or cowed by his centuries of additional life experience. That he should care for such an intriguing, paradoxical figure made perfect sense, as did his decision, in a post-Rose world, to skip inviting her on the TARDIS, opting to visit her sporadically throughout several of his own lives. (It’s easy to make your relationship last forever if what’s been decades between visits for you has been mere days for her.)
Unfortunately, like many aspects of the Moffat era, there eventually was a little too much of a good thing. Each reappearance of River made her existence more confusing, rewriting and introducing new elements into her story seemingly at random. By the time it was revealed she was actually Amy and Rory’s stolen baby who had been secretly trained as an assassin as well as their childhood friend named Mel, her overly complicated story was much more tiring than fun.
Best episode: Season 4’s “The Silence in the Library.” Half of the two-parter that introduced us to River in the first place, these episodes represent the character at her brilliant, capable, secret-keeping best. While many of River’s later appearances became bogged down in the twisty nature of her own timeline, her debut story has somehow only become better with age. Full of terrifying monsters, the episode offers us a tantalizing look at her relationship with the Doctor and sees River sacrifice herself to save him.