5. Alfie (Closing Time)
The Doctor lands in London, about 25 years in the future. Naturally, he finds a bit of trouble, and is investigating it when he happens upon a young man doing the same thing. But the kicker is, this kid knows exactly who and what the Doctor is. How does he know the Doctor? Please, he's heard stories about the Doctor for as long as he can remember. Because he's Alfie Owens, son of Craig. And then they dematerialize together off into the sunset and have magical adventures. I like the idea of having a character who shows the influence that the Doctor has on the lives of people he helps. Of course Craig would tell his son about the madman with a box who helped him save the world. And yeah, maybe that little boy would grow up curious about this mysterious figure, and might become interested in the world-saving business himself. Maybe he could even work for UNIT. Seriously, guys, there's nothing but possibilities here.