The Curator
From Tardis Wiki, the free Doctor Who reference
The curator of the National Gallery in London was a mysterious individual who had insight into a particular Time Lord painting. He spoke with the Eleventh Doctor and told him that the name of the picture was in fact Gallifrey Falls No More, and pointed the Doctor in the direction of a search for Gallifrey.
The man then made some ambiguous references to possibly being the Doctor once, or that the Doctor was just a version of him. (TV: The Day of the Doctor)
Behind the scenes
The line between parody and narrative is very narrow around this character. Obviously the audience are meant to believe that this is, in some indefinable sense, an iteration of the Fourth Doctor. Nothing in the narrative, however, makes such an explicit connection.
