Re: The Curator.... Who is he? (SPOILERS for "The Day of the Doctor")
I think you'd have to be intentionally obtuse not to see the obvious: the Curator is the final Doctor. There's really no ambiguity. He gives Eleven(Twelve) hope that Trenzalore isn't as fixed a final resting place as it might appear.
Some say that if you get Amazon Prime he will hand-deliver your packages during a powerslide in a classic Jag and that he's paid with bottles of octane booster.
All we know is, he's not The Stig but he is The Stig's non-trademarked generic cousin.