5. Caecilius
A last minute additional to my list and one that may have you scratching your heads. Cecilius, as you may remember, lived in Pompeii during the eruption of Mount Vesuvius. He was saved, along with his family, by the Tenth Doctor and Donna, brought onboard the Tardis and relocated to Rome. You would naturally assume his story ended there...however, there's the little fact that Caecilius was played by future Doctor Twelve Peter Capaldi. Secondly, Moffat has hinted that there will be an explanation as to why both the new Doctor and this Roman marble trader look the one and the same. In the last couple of days, Moffat dropped this little tidbit...
"We are aware that Peter Capaldi's played a part in Doctor Who before and we're not going to ignore the fact. "I'll let you in on this. I remember Russell told me he had a big old plan as to why there were two Peter Capaldis in the Who universe, one in Pompeii and one in Torchwood. When I cast Peter, got in touch to say how pleased he was I said 'Okay, what was your theory and does it still work?' and he said 'Yes it does, here it is'. So I don't know if we'll get to it... we'll play that one out over time. It's actually quite neat"."
So, what could that connection be? The two most obvious answers are 1) Caecilius (and Frobisher) were in fact the Doctor...but that doesn't work based on a whole host of reasons. (Such as why didn't he react to Doctor Ten and Donna, and why did Frobisher go and shoot himself, his wife and his children...a very un-Doctor thing to do surely?) 2) Is that they are fragments of the Doctor somehow, split across space and time...but oh wait...that's what they've done with Clara. So what is the reason? Frankly, I can't get my head round it, but I'm excited to find out. Let's hope we get to see Caeilius one more time? Perhaps an explanation too for why a certain soothsayer also looked like Amy Pond?