The show is a significant part of British popular culture, and elsewhere it has gained a cult following. It has influenced generations of British television professionals, many of whom grew up watching the series. The programme originally ran from 1963 to 1989. There was an unsuccessful attempt to revive regular production in 1996 with a backdoor pilot, in the form of a television film titled Doctor Who. The programme was relaunched in 2005, and since then has been produced in-house by BBC Wales in Cardiff. Doctor Who has also spawned numerous spin-offs, including comic books, films, novels, audio dramas, and the television series Torchwood (2006–2011), The Sarah Jane Adventures (2007–2011), K-9 (2009–2010), and Class (2016), and has been the subject of many parodies and references in popular culture.
Thirteen actors have headlined the series as the Doctor. The transition from one actor to another is written into the plot of the show with the concept of regeneration into a new incarnation, a plot device in which a Time Lord "transforms" into a new body when the current one is too badly harmed to heal normally. Each actor's portrayal is unique, but all represent stages in the life of the same character, and together, they form a single lifetime with a single narrative. The time-travelling feature of the plot means that different incarnations of the Doctor occasionally meet. The Doctor is currently portrayed by Jodie Whittaker, who took on the role after Peter Capaldi's exit in the 2017 Christmas special "Twice Upon a Time".
Doctor Who follows the adventures of the title character, a rogue Time Lord from the planet Gallifrey who goes by the name "the Doctor". The Doctor fled Gallifrey in a stolen TARDIS ("Time and Relative Dimension in Space"), a time machine that travels by materialising into and dematerialising out of the time vortex. The TARDIS has a vast interior but appears smaller on the outside, and is equipped with a "chameleon circuit" intended to make the machine take on the appearance of local objects as a disguise; due to a malfunction, the Doctor's TARDIS remains fixed as a blue British police box.
Across time and space, the Doctor's many incarnations often find events that pique their curiosity and try to prevent evil forces from harming innocent people or changing history, using only ingenuity and minimal resources, such as the versatile sonic screwdriver. The Doctor rarely travels alone and often brings one or more companions to share these adventures. These companions are usually humans, owing to the Doctor's fascination with planet Earth, which also leads to frequent collaborations with the international military task force UNIT when the Earth is threatened. The Doctor is centuries old and, as a Time Lord, has the ability to regenerate in case of mortal damage to the body, taking on a new appearance and personality. The Doctor has gained numerous reoccurring enemies during their travels, including the Daleks, the Cybermen, and the Master, another renegade Time Lord.