The Curator

The curator was an elderly incarnation of the Doctor.

Foreshadowing
When the Eleventh Doctor's timeline became distorted, the Curator was seen as one of his future incarnations. (COMIC: The Then and the Now)

Gallifrey falls no more
He met the Eleventh Doctor in the National Gallery in London, and showed insight into a particular Time Lord painting. After the Eleventh Doctor remembered his face (which resembled that of the Fourth Doctor), the curator told him that "in years to come, you might find yourself… revisiting a few. But just the old favourites, eh?"

He spoke with the Eleventh Doctor and told him that the name of the painting was neither No More nor Gallifrey Falls but in fact Gallifrey Falls No More, and pointed the Doctor in the direction of a search for Gallifrey, telling him he had "a lot to do". He congratulated the Doctor on his success.

The curator then told the Doctor "perhaps I was you," or that the Doctor had once been him. (TV: The Day of the Doctor)

Appearance
The Curator had the appearance of an elderly version of the Fourth Doctor. He walked with a cane and wore a cravat under his shirt. (TV: The Day of the Doctor)

Behind the scenes

 * The script never directly states that this character is the Doctor, but hints that he may be a future incarnation who has adopted the same form as his fourth, or is in fact said previous incarnation. COMIC: The Then and the Now later depitcs him as a future incarnation of the Doctor when the Doctor's timeline becomes distorted.
 * Tom Baker is not separately credited for this performance, receiving only a credit for playing "the Doctor" (as did all the other past Doctor actors, who appeared in the episode through the use of archive footage).
 * Early in the episode Queen Elizabeth I's letter appoints the Doctor as "curator of the Under-Gallery."
 * The Curator states that he acquired the painting "under remarkable circumstances", and yet Queen Elizabeth I had instructions regarding it.
 * Tom Baker played a similar nameless character, with the appearance of an older Fourth Doctor, in a series of idents for the 1999 Doctor Who Night. Like the Curator, he is never stated to be the Doctor and refers to him in the third-person, but is shown in the TARDIS and says that he's "called Paul McGann in this one" when introducing the TV movie. He also similarly appeared as the narrator for the unfinished links of Shada, speaking as the Doctor in an exhibition of the monsters he fought while also acknowledging the actors and Shada's cancellation.

Conservateur (The Day of the Doctor) Curador (The Day of the Doctor)