Donna Noble
Donna Noble is amazing. Full stop. Her big mouth and equally big heart make her one of the most simultaneously entertaining and heartwarming of all companions. She takes guff from no one, and there’s no one she won’t help. Donna also represents the best of the companion in modern-day Doctor Who, developing from an insecure secretary into, quite literally, the “most important woman in the whole wide universe.” She becomes so much the Doctor’s equal that by the end of her journey she has to have her memory wiped in order to save her life. (A development that was especially heartbreaking precisely because we all knew – and had seen – how far Donna had come, and how much she’d grown. Taking that all away from her? Whew. Tears.)
Another great aspect of Donna’s time in the TARDIS was her relationship with the Doctor. Ten had been romantically connected to both his previous companions – he’d loved Rose Tyler and lost her, and couldn’t return the affections of one Martha Jones (who was probably too good for him anyway). Donna was not here for any of that – and said so, frequently. She and Ten had a perfect best mates quality to their relationship that felt refreshing and real, and was exactly what we all – both viewers and characters – needed at the time.
Best episode: Season 4’s “Turn Left.” After a mystical beetle attaches itself to her back, Donna becomes part of an alternate universe in which she never met the Doctor and we learn just how bad that would have been for both her and the world at large. Catherine Tate gets the chance to play it straight in this episode, as Donna figures out what’s going on and sacrifices herself to fix the timeline, with a little help from a dimension-hopping Rose Tyler.