The Curator

The Curator was an elderly incarnation of the Doctor who had retired from his adventurous ways to become "a humble curator." He curated the Under-Gallery, where he watched over the painting Gallifrey Falls No More after acquiring it under "remarkable circumstances."

Foreshadowing
When encountering the "Vortex Butterfly", the Tenth Doctor was cryptically told that he would not be "limited" to "thirteen lives". (COMIC: Vortex Butterflies)

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

When Captain Lundvik threatened to shoot him, the Twelfth Doctor speculated that he would "keep on regenerating forever" if he was executed. (TV: Kill the Moon) Rassilon would later state his own uncertainty to the number of regenerations the Doctor had been granted. (TV: Hell Bent)

Getting a painting
Under "remarkable circumstances," the Curator was able to acquire Gallifrey Falls No More and brought it to the Under-Gallery. (TV: The Day of the Doctor)

Interaction with his eleventh incarnation
When his war, tenth and eleventh incarnations rendezvoused at the National Gallery after the final battle of the Last Great Time War, the Curator approached Clara Oswald, telling her he was looking for the Doctor.

When the Eleventh Doctor was alone, the Curator made his presence known when the Doctor noted how he could retire and be a curator, with the Curator exclaiming that he "really [thought] [the Doctor] might." Stunned by how familiar the Curator was, the Doctor noted that he "never forget[s] a face", the Curator merely noted that the Doctor would revisit a few in years to come but just the "old favourites".

He told the Doctor that the name of the painting was neither No More nor Gallifrey Falls, but in fact one title; Gallifrey Falls No More. Despite proclaiming to be a "humble curator [who] wouldn't really know", he told the Doctor that Gallifrey was lost, and pointed him in the direction to search for it, telling him he had "a lot to do" and congratulated the Doctor.

When the Doctor tried to pry into his meaning, the Curator retaliated by pointing out it was the Doctor's choice. He was then about to tell the Doctor what he would do if he was him, but then teasingly said that "perhaps [he] was [him]," or that maybe the Doctor had been him, before deciding that it "[didn't] matter either way" and left. (TV: The Day of the Doctor)

Appearance
Having the appearance of an elderly Fourth Doctor, the Curator's face was wrinkled with baggy cheeks, a hooked nose and a pronounced throat. He had light blue eyes and big ears with dangling ear lobes.

Though he was balding, his hair was completely white, and his eyebrows were non-existent. (TV: The Day of the Doctor)

Clothing
The Curator wore a dark olive green blazer, a checked white shirt, mahogany red trousers and brown slip-on shoes with white socks. In his blazer breast pocket, he kept a red handkerchief. He also walked with a cane and wore a blue cravat under his shirt. (TV: The Day of the Doctor)

Behind the scenes

 * The script for The Day of the Doctor 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 the Fourth Doctor. The Then and the Now later depicts him as a future incarnation of the Doctor when the Doctor's timeline becomes distorted.
 * In the above scene he appears at the opposite end of the Doctor's lifespan to the First Doctor; this implies the Curator to be the final incarnation of the Doctor.
 * In an early draft of The Day of the Doctor, the Moment as portrayed by Billie Piper was the one to play the role of the Curator. Moffat considered that the Curator could still be interpreted as the Moment interacting with the Doctor using the Fourth Doctor's appearance.
 * 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).
 * In DWM 487, Showrunner Steven Moffat confirms in the magazine's regular "Ask Steven" feature that the Curator is intended to be a future incarnation of the Doctor and suggests that, just as the War and Tenth Doctors retain no memory of the events of The Day of the Doctor, the Eleventh Doctor would not remember the specifics of his conversation with the Curator but will leave the Under-Gallery "with the strange, groundless conviction that Gallifrey is still out there". However as with many revelations made in this feature, and by Moffat's own admission, this is not an in-universe explanation for the character until such a time as it appears in an in-universe source.
 * Moffat once stated that his preferred interpretation of the character, is to be the Doctor in a very distant future who settled down and chose a different incarnation per day to revisit.
 * Tom Baker previously played nameless characters suggested to be future incarnations of the Doctor.
 * In a series of idents for the 1999 Doctor Who Night, Baker's character referred to the Doctor in the third person but walked through in the Doctor's TARDIS and mentioned that he was "called Paul McGann in this one" when introducing TV: Doctor Who. He encountered multiple Daleks in the TARDIS before he introduced a "night of pure entertainment". This character was forgetful and consequently found himself laughing at most situations; he wore a black suit jacket, an open-neck shirt, and a white cravat.
 * Baker also played the narrator for the unfinished links of the 1992 release of Shada. He described this adventure of his as "cancelled", and he mentioned that he had once defeated the Cybermen, Daleks, and Davros. He wore a pin stripe suit, a blue shirt, and a floral tie.
 * The Curator was dubbed in Germany by voice actor Michael Schwarzmaier who is the official dubbing voice for all classic Doctors.
 * Despite Big Finish's license being expanded to include the new series of Doctor Who, the BBC specifically instructed them not to use the Curator character in their audio dramas.