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 daylight savings time was implemented to give him another hour of track time and that he goes through Pon Farr every 7 seconds.
All we know is, he's called The Stig.