Also:
"The current theories range from the idea that John Hurt is playing the man who became the First Doctor. That is he is the man who did something that caused The Doctor to make the promise that he not only stole the TARDIS, but took the name The Doctor.
Another theory is that Hurt is playing the true Ninth Doctor and that Smith is the Twelfth and not the Eleventh. This is certainly a possibility given what we know about The Doctor, but it does create the problem with the fact that the next regeneration would be The Doctor’s last…unless, of course, it turns out that River giving up all of her regenerations extended the life of The Doctor well beyond the norm for a Time Lord""