Created by Sydney Newman, C. E. Webber and Donald Wilson

Doctor Who is a British science-fiction television programme produced by the BBC since 1963. The programme depicts the adventures of a Time Lord called "the Doctor", an extraterrestrial being from the planet Gallifrey. The Doctor explores the universe in a time-travelling space ship called the TARDIS. Its exterior appears as a blue British police box, which was a common sight in Britain in 1963 when the series first aired. Accompanied by a number of companions, the Doctor combats a variety of foes, while working to save civilisations and help people in need.
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.
Twelve 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 – an idea introduced in 1966 to allow the show to continue after the departure of original lead William Hartnell who was becoming very ill at the time. The concept is that this is a Time Lord trait through which the character of the Doctor takes on a new body and personality to recover from a severe injury or anything that would otherwise kill a normal person. Each actor's portrayal differs, but all represent stages in the life of the same character and form a single narrative. The time-travelling feature of the plot means that different incarnations of the Doctor occasionally meet. The current lead, Peter Capaldi, confirmed he would be leaving the show after the tenth series, with his final appearance being the 2017 Christmas special, "Twice Upon a Time". In July, Jodie Whittaker was announced as the Thirteenth Doctor, the first woman to be cast in the role.

Doctor Who first appeared on BBC television at 17:16:20 GMT on 23 November 1963, following discussions and plans that had been in progress for a year. The Head of Drama, Canadian Sydney Newman, was mainly responsible for developing the programme, with the first format document for the series being written by Newman along with the Head of the Script Department (later Head of Serials) Donald Wilson and staff writer C. E. Webber. Writer Anthony Coburn, story editor David Whitaker and initial producer Verity Lambert also heavily contributed to the development of the series. The series' title theme was composed by Ron Grainer and realised by Delia Derbyshire of the BBC Radiophonic Workshop. The programme was originally intended to appeal to a family audience. The BBC drama department's Serials division produced the programme for 26 seasons, broadcast on BBC One. Falling viewing numbers, a decline in the public perception of the show and a less prominent transmission slot saw production suspended in 1989 by Jonathan Powell, Controller of BBC One. Although (as series co-star Sophie Aldred reported in the documentary Doctor Who: More Than 30 Years in the TARDIS) it was effectively, if not formally, cancelled with the decision not to commission a planned 27th series of the show for transmission in 1990, the BBC repeatedly affirmed that the series would return.

 While in-house production had ceased, the BBC hoped to find an independent production company to relaunch the show. Philip Segal, a British expatriate who worked for Columbia Pictures' television arm in the United States, had approached the BBC about such a venture as early as July 1989, while the 26th series was still in production. Segal's negotiations eventually led to a Doctor Who television film, broadcast on the Fox Network in 1996 as a co-production between Fox, Universal Pictures, the BBC and BBC Worldwide. Although the film was successful in the UK (with 9.1 million viewers), it was less so in the United States and did not lead to a series.

 Licensed media such as novels and audio plays provided new stories, but as a television programme Doctor Who remained dormant until 2003. In September of that year, BBC Television announced the in-house production of a new series after several years of attempts by BBC Worldwide to find backing for a feature film version. The executive producers of the new incarnation of the series were writer Russell T Davies and BBC Cymru Wales Head of Drama Julie Gardner. It has been sold to many other countries worldwide.

 Doctor Who finally returned with the episode "Rose" on BBC One on 26 March 2005. There have since been four further series in 2006–8 and 2010, and Christmas Day specials every year since 2005. No full series was filmed in 2009 although four additional specials starring David Tennant were made. A fifth full-length series began in spring 2010, with Steven Moffat replacing Davies as head writer and executive producer.

 The 2005 version of Doctor Who is a direct continuation of the 1963–1989 series, as is the 1996 telefilm. This differs from other series relaunches that have either been reimaginings or reboots (for example, Battlestar Galactica and Bionic Woman) or series taking place in the same universe as the original but in a different time period and with different characters (for example, Star Trek: The Next Generation and spin-offs).

 Doctor Who originally ran for 26 series on BBC One, from 23 November 1963 until 6 December 1989. During the original run, each weekly episode formed part of a story (or "serial") — usually of four to six parts in earlier years and three to four in later years. Notable exceptions were the epic The Daleks' Master Plan, which aired in 12 episodes (plus an earlier one-episode teaser, "Mission to the Unknown", featuring none of the regular cast), almost an entire series of 7-episode serials (series 7), the 10-episode serial The War Games, and The Trial of a Time Lord, which ran for 14 episodes (albeit divided into three production codes and four narrative segments) during Series 23. Occasionally serials were loosely connected by a storyline, such as Series 8 being devoted to the Doctor battling a rogue Time Lord called The Master, Series 16's quest for The Key to Time, Series 18's journey through E-Space and the theme of entropy, and Series 20's Black Guardian Trilogy.

 The programme was intended to be educational and for family viewing on the early Saturday evening schedule. Initially, it alternated stories set in the past, which taught younger audience members about history, with stories set either in the future or in outer space to teach them about science. This was also reflected in the Doctor's original companions, one of whom was a science teacher and another a history teacher.

However, science fiction stories came to dominate the programme and the "historicals", which were not popular with the production team, were dropped after The Highlanders (1967). While the show continued to use historical settings, they were generally used as a backdrop for science fiction tales, with one exception: Black Orchid set in 1920s England.

The early stories were serial-like in nature, with the narrative of one story flowing into the next, and each episode having its own title, although produced as distinct stories with their own production codes. Following The Gunfighters (1966), however, each serial was given its own title, with the individual parts simply being assigned episode numbers. What to name these earlier stories is often a subject of fan debate

 Of the programme's many writers, Robert Holmes was the most prolific, while Douglas Adams became probably the most well-known outside Doctor Who itself, due to the popularity of his Hitchhiker's Guide to the Galaxy.

 The serial format changed for the 2005 revival, with each series usually consisting of 13 45-minute, self-contained episodes (60 minutes with adverts, on overseas commercial channels), and an extended episode broadcast on Christmas Day. Each series includes several standalone and multi-part stories, linked with a loose story arc that resolves in the series finale. As in the early "classic" era, each episode, whether standalone or part of a larger story, has its own title. Occasionally, regular-season episodes will exceed the 45-minute run time; examples have included the episodes "Journey's End" from 2008 and "The Eleventh Hour" from 2010, both of which exceeded an hour in length.

 778 Doctor Who instalments have been televised since 1963, ranging between 25-minute episodes (the most common format), 45-minute episodes (for Resurrection of the Daleks in the 1984 series, a single season in 1985, and the revival), two feature-length productions (1983's "The Five Doctors" and the 1996 television film), five 60-minute Christmas specials, and four specials ranging from 60 to 75 minutes in 2007 and 2009. Two mini-episodes, running about eight minutes each, were also produced for the 2005 and 2007 Children in Need charity appeals, while another mini episode was produced in 2008 for a Doctor Who-themed edition of The Proms. A two-part mini-episode was also produced for the 2011 edition of Comic Relief.

Between about 1964 and 1973, large amounts of older material stored in the BBC's various video tape and film libraries were either destroyed, wiped or suffered from poor storage which led to severe deterioration from broadcast quality. This included many old episodes of Doctor Who, mostly stories featuring the first two Doctors: William Hartnell and Patrick Troughton. Following consolidations and recoveries the archives are complete from the programme's move to colour television (starting from Jon Pertwee's time as the Doctor), although a few Pertwee episodes have required substantial restoration; a handful have been recovered only as black-and-white films, and several survive in colour only as NTSC copies recovered from North America. In all, 106 of 253 episodes produced during the first six years (most notably series 3, 4, & 5, from which 90 episodes are missing) of the programme are not held in the BBC's archives. In 1972 almost all episodes then made were known to exist at the BBC, while by 1978 the practice of wiping tapes and destroying 'spare' film copies had ended.

 No 1960s episodes exist on their original videotapes (all surviving copies being film copies), though some were transferred to film for editing before transmission, and these hence exist as originally transmitted.

 Some episodes have been returned to the BBC from the archives of other countries who bought copies for broadcast, or by private individuals who acquired them by various means. Early colour videotape recordings made off-air by fans have also been retrieved, as well as excerpts filmed from the television screen onto 8 mm cine film and clips that were shown on other programmes. Audio versions of all of the lost episodes exist from home viewers who made tape recordings of the show.

 In addition to these, there are off-screen photographs made by photographer John Cura, who was hired by various production personnel to document many of their programmes during the 1950s and 1960s, including Doctor Who. These have been used in fan reconstructions of the serials. These amateur reconstructions have been tolerated by the BBC, provided they are not sold for profit and are distributed as low quality VHS copies.

 One of the most sought-after lost episodes is Part Four of the last William Hartnell serial, "The Tenth Planet" (1966), which ends with the First Doctor transforming into the Second. The only portion of this in existence, barring a few poor quality silent 8 mm clips, is the few seconds of the regeneration scene, as it was shown on the children's magazine show Blue Peter. With the approval of the BBC, efforts are now under way to restore as many of the episodes as possible from the extant material. Starting in the early 1990s, the BBC began to release audio recordings of missing serials on cassette and compact disc, with linking narration provided by former series actors.

 "Official" reconstructions have also been released by the BBC on VHS, on MP3 CD-ROM and as a special feature on a DVD. The BBC, in conjunction with animation studio Cosgrove Hall has reconstructed the missing Episodes 1 and 4 of "The Invasion" (1968), using remastered audio tracks and the comprehensive stage notes for the original filming, for the serial's DVD release in November 2006. Although no similar reconstructions have been announced as of 2010, Cosgrove Hall has expressed an interest in animating more lost episodes in the future. Announced in June 2011, the missing episodes of The Reign of Terror will be animated by animation company Theta-Sigma in collaboration with Big Finish.

 In April 2006, Blue Peter launched a challenge to find these missing episodes with the promise of a full scale Dalek model as a reward.

 In December 2011 it was announced that part 3 of Galaxy 4 and part 2 of The Underwater Menace had been returned to the BBC by a fan who had purchased them in the mid-1980s without realising that the BBC did not hold copies.

As a Time Lord, the Doctor has the ability to regenerate his body when near death. Introduced into the storyline as a way of continuing the series when the writers were faced with the departure of lead actor William Hartnell in 1966, it has continued to be a major element of the series, allowing for the recasting of the lead actor when the need arises. The serials The Deadly Assassin and Mawdryn Undead and the 1996 TV film suggest that a Time Lord can regenerate 12 times, for a total of 13 incarnations. However at least one Time Lord — the Master — managed to circumvent this (in The Keeper of Traken).

 The Doctor has fully gone through this process and its resulting after-effects on ten occasions, with each of his incarnations having their own quirks and abilities but otherwise sharing the consciousness, memories, experience and basic personality of the previous incarnations.

 The Doctor almost always shares his adventures with up to three companions, and since 1963 more than 35 actors have been featured in these roles. The First Doctor's original companions were his granddaughter Susan Foreman (Carole Ann Ford) and school teachers Barbara Wright (Jacqueline Hill) and Ian Chesterton (William Russell). The only story from the original series in which the Doctor travels alone is The Deadly Assassin.

 Dramatically, the companions' characters provide a surrogate with whom the audience can identify, and serve to further the story by requesting exposition from the Doctor and manufacturing peril for the Doctor to resolve. The Doctor regularly gains new companions and loses old ones; sometimes they return home or find new causes — or loves — on worlds they have visited. Some have even died during the course of the series.

 Although the majority of the Doctor's companions have been young, attractive women, the production team for the 1963–89 series maintained a long-standing taboo against any overt romantic involvement in the TARDIS. The taboo was controversially broken in the 1996 television film when the Eighth Doctor was shown kissing companion Grace Holloway.

 Previous companions have reappeared in the series. One former companion, Sarah Jane Smith (played by Elisabeth Sladen), together with the robotic dog K-9, appeared in an episode of the 2006 series nearly 13 years after their last appearances in the 30th-anniversary story "Dimensions in Time" (1993). Sladen also starred as the character in an independent film spin-off, Downtime, in 1995. Afterward, the character was featured in the spin-off series The Sarah Jane Adventures. Sladen once again appeared as Sarah Jane in the final two episodes of the fourth series of the new Doctor Who, and again appearing briefly in the 2009 Christmas special The End of Time.

 The companions of the 10th Doctor included a large ensemble, many of whom reappeared in "Journey's End" and/or the 2009 Christmas special The End of Time.

Spin-offs

Doctor Who has appeared on stage numerous times. In the early 1970s, Trevor Martin played the role in Doctor Who and the Daleks in the "Seven Keys to Doomsday". In the late 1980s, Jon Pertwee and Colin Baker both played the Doctor at different times during the run of a play titled Doctor Who – The Ultimate Adventure. For two performances, while Pertwee was ill, David Banks (better known for playing Cybermen) played the Doctor. Other original plays have been staged as amateur productions, with other actors playing the Doctor, while Terry Nation wrote The Curse of the Daleks, a stage play mounted in the late 1960s, but without the Doctor.

 A pilot episode ("A Girl's Best Friend") for a potential spinoff series, K-9 and Company, was aired in 1981 with Elisabeth Sladen reprising her role as companion Sarah Jane Smith and John Leeson as the voice of K-9, but was not picked up as a regular series.

 The Doctor has also appeared in webcasts and in audio plays; prominent among the latter were those produced by Big Finish Productions from 1999 onwards, who were responsible for a range of audio plays released on CD, as well as 2006's eight-part BBC 7 series starring Paul McGann.

 Following the success of the 2005 series produced by Russell T Davies, the BBC commissioned Davies to produce a 13-part spin-off series titled Torchwood (an anagram of "Doctor Who"), set in modern-day Cardiff and investigating alien activities and crime. The series debuted on BBC Three on 22 October 2006. John Barrowman reprised his role of Jack Harkness from the 2005 series of Doctor Who. Two other actresses who appeared in Doctor Who also star in the series; Eve Myles as Gwen Cooper, who also played the similarly named servant girl Gwyneth in the 2005 Doctor Who episode "The Unquiet Dead", and Naoko Mori who reprised her role as Toshiko Sato first seen in "Aliens of London". A second series of Torchwood aired in 2008; for three episodes, the cast was joined by Freema Agyeman reprising her Doctor Who role of Martha Jones. A third series was broadcast from 6 to 10 July 2009, and consisted of a single five-part story called "Children of Earth". A fourth series, "Torchwood: Miracle Day" jointly produced by BBC Wales, BBC Worldwide and the American entertainment company Starz debuted in 2011 and left the usual Cardiff setting for the first time.

 The Sarah Jane Adventures, starring Elisabeth Sladen who reprised her role as Sarah Jane Smith, was developed by CBBC; a special aired on New Year's Day 2007 and a full series began on 24 September 2007. A second series followed in 2008, notable for featuring the return of Brigadier Lethbridge-Stewart. A third and fourth series aired in the autumn of 2009 and 2010 respectively.

 An animated serial, "The Infinite Quest", aired alongside the 2007 series of Doctor Who as part of the children's television series "Totally Doctor Who". The serial featured the voices of series regulars David Tennant and Freema Agyeman but is not considered part of the 2007 series. A second animated serial, "Dreamland", aired in six parts on the BBC Red Button service, and the official Doctor Who website in 2009.

 Numerous other spin-off series have been created not by the BBC but by the respective owners of the characters and concepts. Such spin-offs include the Faction Paradox, Iris Wildthyme, Bernice Summerfield and P.R.O.B.E. series plus others including the current K-9 television series, currently airing on Disney XD.

 Announced on 20 October 2011, a new audio spin-off series titled Counter-Measures will be released in July 2012. The series is set in 1964 and centers on the characters Captain Gilmore, Rachel Jensen and Allison from the story "Remembrance of the Daleks" who have been commissioned by the government to be part of a new specialist group to investigate unexplained phenomena and new dangerous technology.