Science fiction television in the context of "Fifteenth Doctor"

The Doctor, sometimes known as Doctor Who, is the protagonist of the long-running BBC science fiction television series Doctor Who. An extraterrestrial Time Lord, the Doctor travels the universe in a time travelling spaceship called the TARDIS, often with companions. Since the show's inception in 1963, the character has been portrayed by fourteen lead actors. The transition to each succeeding actor is explained within the show's narrative through the plot device of regeneration, a biological function of Time Lords that allows a change of cellular structure and appearance with recovery following a mortal injury.

A number of other actors have played the character in stage and audio plays, as well as in various film and television productions. The Doctor has also been featured in films and a vast range of spin-off novels, audio dramas and comic strips.

The Time Lords are a fictional ancient race of extraterrestrial people in the British science fiction television series Doctor Who. In-universe, they hail from the planet Gallifrey and are stated to have invented time travel technology. They have sworn an oath to not interfere in the universe; those who reject this and leave the planet to live in the universe are referred to as "renegades". One of their number, the Doctor, fled Gallifrey, stealing one of their time machines known as a TARDIS. In the early days of the series, the Time Lords were not initially referred to, and though the Doctor was stated to be non-human, the character did not clarify beyond that. The Time Lords, as well as the Doctor's affiliation with them, first appeared in the 1969 serial The War Games. Following this appearance, the Time Lords serve as recurring characters, with many individual Time Lords serving either antagonistic or supporting roles in the series. Following the show's 2005 revival, it is revealed the Time Lords had been wiped out in-universe, killed by the Doctor during the events of a war against a species known as the Daleks. Though the Doctor is later able to go back and save the Time Lords in the 2013 episode "The Day of the Doctor", they are killed again by the antagonist the Master during the events of the 2020 episode "Spyfall".

The Time Lords originally did not exist in the series' narrative, though the Doctor referred to not being human. When creating 1969 serial The War Games, the production team needed a way to resolve the narrative of the serial in a satisfying manner. The team decided to have him meet his own people to bring the narrative back to the Doctor's origins. The Time Lords are believed to have been conceived by producer Derrick Sherwin, who initially had assumed they were a pre-existing element in the series. Sherwin discussed and planned out the Time Lords' role with co-writer Terrance Dicks, laying the groundwork for the Time Lords' future appearances in the series. Though the Time Lords were initially portrayed as god-like figures, they were recontextualised significantly by the 1976 serial The Deadly Assassin. The serial depicted them as having internal political struggles, with Time Lords being hypocritical and corrupt in their nature. The serial also established a distinct visual identity for the Time Lord race, having them wear ceremonial robes and large collars. This depiction of the Time Lords would be maintained throughout the rest of the show's original run. The show's 2005 revival would end up killing the Time Lord race due to showrunner Russell T Davies finding the Time Lords boring, while also wanting to establish them as mythological figures in the series' lore. The following showrunner, Steven Moffat, would bring them back to establish a new character arc for the Doctor, allowing the character to move on from their guilt caused by their actions in destroying them.

The TARDIS (/ˈtɑːrdɪs/; acronym for "Time And Relative Dimension(s) In Space") is a fictional hybrid of a time machine and spacecraft that has, since 1963, appeared in the British science fiction television series Doctor Who and its various spin-offs. While a TARDIS is capable of disguising itself, the exterior appearance of the Doctor's TARDIS typically mimics a police box, an obsolete type of telephone kiosk that was once commonly seen on streets in Britain in the 1940s and 50s. Its interior is shown as being much larger than its exterior, commonly described as being "bigger on the inside".

Due to the significance of Doctor Who in popular British culture, the shape of the police box is now more strongly associated with the TARDIS than its real-world inspiration. The name and design of the TARDIS is a registered trademark of the British Broadcasting Corporation (BBC), although the design was originally created by the Metropolitan Police Service.

Fourteen actors have portrayed the Doctor in a leading role in the British science fiction television series Doctor Who. The series' protagonist, the Doctor is an alien from a species called Time Lords. The transition to each succeeding actor is explained within the narrative through the plot device of regeneration, which allows Time Lords a change of cellular structure when they near death, changing their appearance and personality. The first actor to portray the Doctor was William Hartnell beginning with An Unearthly Child (1963) through The Tenth Planet (1966). In the final moments of the serial, the First Doctor regenerated into Patrick Troughton's Second Doctor.

The most recent incarnation, the Fifteenth Doctor, was played by Ncuti Gatwa, who took over the role from David Tennant following the conclusion of "The Giggle" (2023). Gatwa departed the role in "The Reality War" (2025).