Moffat recently addressed John Hurt‘s incarnation of the Doctor — from his persona to his apparent age to his multilayered costume — with SFX:
“I always think that the clown and hero are different levels in the Doctor — there is no completely straight Doctor. The folk memory of [William] Hartnell is he’s a cranky old man, but when you watch him he plays the Doctor as a stroppy child; very twinkly. And he’s not crotchety, he’s sulky, the way that an infant would be. Ian and Barbara are sort of his parents, indulging him to go and behave himself a bit better. The Doctors are always like that. He’s either an extraordinarily youthful old man or an extraordinarily old young man. He’s always both.