6. Susan Foreman (Campbell), The Doctor's Granddaughter
The Character: It's still occasionally news to fans of new Who that the Doctor is, or at least was, a grandfather. This implies that he was also a father, and probably a husband, too. Logically he also has parents, Looms not withstanding. But Susan remains the only part of the Doctor's family we've seen before. Susan was the original companion; traveling with the Doctor from moment one. She was also the first to leave, electing to remain behind on 22nd century Earth to help the planet recover from a Dalek invasion, and to be with a young man she'd fallen in love with. Aside from an appearance in "The Five Doctors", the character was neither seen nor heard from again. Well, except in the audios, which also gave us the doctor's great-grandson, but that's a subject for a different article. Bringing Susan back onto the screen would be a delight. She very likely returned to Gallifrey during the Time War, since it sounds as though pretty much all the Time Lords were involved. And yes, I'm assuming she was indeed a Time Lord, just like the Doctor. There is no reason to assume anything other than her being the Doctor's biological granddaughter.
Who Should Play Her:
I'd like to keep Susan fairly young-looking, so a British actress in her twenties would be just about right. How about Emma Watson? I think she could do a job bringing some intensity to the character when needed, but it wouldn't seem especially out of place for her to refer to the Capaldi Doctor as "Grandfather" (on a side note, "By Capaldi's Eyebrows!" may be the best exclamation ever). Emma Watson does, I believe, have the chops for this. She's also just about the perfect age, and is enough of a "name" that having her on the show would be a decent get. But she's not so big that she'd cost a fortune to cast. I really think she'd be an excellent choice.