The Doctor (The Thief of Sherwood)

According to some accounts, the Doctor existed only ever as a fictional creation, as the eponymous character in the BBC science fiction series Doctor Who. (PROSE: The Thief of Sherwood, The Terror of the Umpty Ums) This was also true in multiple meta-fiction universes. (COMIC: TV Action!, The Girl Who Loved Doctor Who)

The titular character was also referred to as "Dr. Who" in the credits for the show and in a synopsis for Radio Times. (PROSE: The Thief of Sherwood) However, the version of the Doctor within David Karpagnon's mind stated she was not allowed to refer to herself as "Doctor Who" onscreen despite the fact she thought the name was brilliant. (PROSE: The Terror of the Umpty Ums)

In 1964, the Doctor was played by William Hartnell. Tom Baker played the Doctor during the 1970s. (PROSE: The Thief of Sherwood) At some point in the 21st century, the Doctor was played by a woman. (PROSE: The Terror of the Umpty Ums)

Fictional biography
The Doctor was a Gallifreyan, (PROSE: The Thief of Sherwood) specifically, a Time Lord. (PROSE: The Terror of the Umpty Ums) He initially traversed the universe with his granddaughter Susan Foreman and later gained two other companions in Ian Chesterton and Barbara Wright. The latter described being "shanghaied into time and space" by the Doctor.

Barbara wrote to her Auntie Margaret about her recent experiences of being poisoned by radiation, hailed as a goddess, possessed by an alien brain and let down by a Frenchman. They had also encountered the Daleks.

On one occasion, the Doctor landed the TARDIS in an abandoned medieval castle during the time of Robin Hood. He was captured by the Merry Men. The Doctor spared Ian from being executed by the Sheriff of Nottingham by posing as an monk. He then secured Ian's release by convincing the Sheriff he could make gold from base substances. When the Sheriff came to observe the Doctor's demonstration the Doctor set light to the mixture causing an explosion and knocking them both unconscious. The Doctor escaped and the Merry Men attacked the Sheriff causing him to flee. After this, the Doctor set the controls in the TARDIS for 1964 but warned of a build up of pressure outside the craft, leading to their next predicament. (PROSE: The Thief of Sherwood)

At some point, the Doctor changed into a woman. By this time she was known to many as the greatest warrior in the universe and had earned the titles "the Oncoming Storm, the Bringer of Darkness, the Imp of the Pandorica and the final victor of the Time War. She had also fought Cybermen, Weeping Angels, Sontarans, and Slitheen.

David Karpagnon, an orphan with dissociative personality disorder, watched the show around this time. A version of the Doctor inside his head managed to convince him that he was not a DeathBorg 400 but a resident of a children's home that he was otherwise going to destroy. (PROSE: The Terror of the Umpty Ums)

Behind the scenes
As well as in stories that give no indication of happening in a different universe, the Doctor existing solely as a character in Doctor Who has been explored in other sources. The Eighth Doctor visited a universe where he discovered his fourth incarnation as a fictional character in TV Action! and the Eleventh Doctor visited a similar universe where he found himself fictional in The Girl Who Loved Doctor Who. Of course, as a significant part of popular culture and Earth history the Doctor as a character in fiction has been explored from other stories within the Doctor's universe such as Sarah Jane Smith's Doctor series.