History TheNthDoctor / DoctorWho

* '''14th''' -- David Tennant (2022-2023)

As such, the eventual "regeneration" process in "[[Recap/DoctorWhoS4E2TheTenthPlanet The Tenth Planet]]" was the writers' second intentional choice for how to change the Doctor, and it's apparent from the episode that they weren't quite sure what they'd stumbled upon. The regeneration of the First into the Second is stated to be "a feature of the TARDIS" (rather than a biological process) and [[RippedFromTheHeadlines inspired by]] [[HigherUnderstandingThroughDrugs 1960s LSD culture]] in how the experience was supposed to permanently alter his mind. The regeneration from the Second to the Third is off-screen and forced upon him by the Time Lords, and marks the first time the new Doctor was shown in his predecessor's costume. The regeneration from the Third to Fourth benefited from [[Creator/BarryLetts a Buddhist producer]] who [[RuleOfSymbolism made a connection with Buddhist teachings on transience and reincarnation and decided to exploit this]], and marks the point where regeneration is explicitly linked to death of the old body.

* [[Recap/DoctorWhoS35E12HellBent "Hell Bent"]] features the general of Gallifrey's armed forces regenerating. He goes from Ken Bones (white man) to T'Nia Miller (black woman). Miller's incarnation notes that Bones' incarnation (the commander's tenth regeneration) was her only male one, confirming that at least some Time Lords do recognize a base gender.

** Regenerated in TheTeaser of [[Recap/DoctorWhoS24E1TimeAndTheRani "Time and the Rani"]], due to unknown injuries received beforehand. There's a lot of official FixFic about that one, the most notable one being in AudioPlay/BigFinishDoctorWho's ''[[Recap/BigFinishDoctorWhoSpecialTheLastAdventure The Sixth Doctor: The Last Adventure]]'', which retcons the opening of "Time and the Rani" such that the lasers shooting at the TARDIS in that scene are the direct cause of the regeneration, and the reason for the regeneration is a HeroicSuicide due to... another long story: The Valeyard (see below) has hatched an AssimilationPlot to replace every Time Lord that has ever existed with himself, starting with the Sixth Doctor, which leaves the Doctor trapped in the Matrix, alone, powerless, and scheduled for death. The Doctor, having run out of time and solutions, learns that the lynchpin to the Valeyard's plans is specifically the Sixth Doctor's mind, thus that regenerating will foil his conquest and save the entire Time Lord race. He therefore sends a mental signal to himself in the past, subtly influencing himself into (this would be the opening scene of "Time and the Rani") deliberately piloting the TARDIS to the planet Lakertya to be shot down by the Rani's laser beams, laced with radioactivity from the planet which he knows is fatal only to Time Lords. On TV, the Sixth Doctor's regeneration was a case of RealLifeWritesThePlot as producer John Nathan-Turner was forced to fire Baker (whom BBC brass had determined was unpopular with viewers) in exchange for a series renewal. Baker, understandably, refused to return to film a regeneration story, and as a result the producers were forced to FakeShemp Sylvester [=McCoy=] as the Sixth Doctor briefly.

Every time the Doctor regenerates, the character undergoes a radical change in characterization, costume, and personality. However, all memories and past experiences of past incarnations remain, along with a certain amount of character stability (they're always going to be quirky and altruistic and fight evil aliens), meaning the Thirteenth, Tenth and Fourth Doctors are the exact same person as the First Doctor and each other, despite looking and acting much differently. Personality is a combination of "nature" and "nurture" — one story said that "Although the aspects of their personality caused by "nurture" would not change, the "nature" contribution to their personality would." The mechanic was implemented back when Creator/WilliamHartnell was playing the First Doctor, and obviously growing too ill to carry on further (plus he wasn't getting along with the current producers and in fact had nearly been fired a couple of times over the preceding year). A decision was made to let him retire and bring in Creator/PatrickTroughton for the role, and the writers decided that since the Doctor is an alien, he could change form into a new body if his current one was giving out. From there, the plot device has been modified into the go-to response for any actor wanting to depart from the role of the Doctor — kill off the current incarnation and regenerate them into the next actor, thus avoiding TheOtherDarrin (itself only invoked for the Doctor in multi-Doctor stories where an earlier incarnation's actor has already died; so far, this has only happened twice, and [[Recap/DoctorWho20thASTheFiveDoctors both]] [[Recap/DoctorWho2017CSTwiceUponATime times]] it was for the First Doctor).

** Yet another long story: in [[Recap/DoctorWhoTVMTheTVMovie the TV movie]], as soon as the Doctor hastily steps out of his TARDIS in San Francisco, a Chinatown gang instinctively guns him down. A gangster named Chang Lee then takes the Doctor to the hospital. There, the staff x-rays the Doctor. His bullet wounds are actually [[MadeOfIron minor]], but the doctors mistake his bicardial cardiovascular system for an x-ray double-exposure and his double-heartbeat for deadly fibrillation. They then try to "save" his life, but his anatomy causes a surgeon to literally probe the Doctor to death. Since the Doctor is under the effects of anesthesia, his regeneration takes place hours after he dies, and as the Eighth Doctor he is left with temporary amnesia afterwards. This has led to some NeverLiveItDown for Eight — being stricken with amnesia for most of his only on-screen story means in books and audio dramas he has a habit of winding up in such situations again.

** The circumstances of his death long [[TheUnrevealed unrevealed]], it is learned in a DVD short called "[[Recap/DoctorWho50thPrequelTheNightOfTheDoctor The Night of the Doctor]]" that he was fatally injured when a spaceship he was on crashed onto the planet Karn, but given a chance at regeneration by the Sisterhood of Karn, who temporarily revived him. The Doctor was able to willingly choose what kind of Time Lord he would turn into with their help, and chose "Warrior" to end the Last Great Time War once and for all. Unusually, this regeneration scene was not filmed until 2013; before that year, fans of the TV series only knew about the Eighth Doctor from the 1996 movie, before the 2005 revival jumped to a new incarnation without much explanation. Though being the "current" Doctor from 1996 to the 2005 {{revival}} in the ExpandedUniverse means that he has — and continues to have — a very healthy run, it never ''was'' known how the Paul [=McGann=] Doctor's life ''ended'', though the Time War was always the most logical assumption to make.

** The circumstances of his death long unrevealed, we learn in a DVD short called [[Recap/DoctorWho50thPrequelTheNightOfTheDoctor "The Night of the Doctor"]] that he was fatally injured when a spaceship he was on crashed onto the planet Karn, but given a chance at regeneration by the Sisterhood of Karn, who temporarily revived him. The Doctor was able to willingly choose what kind of Time Lord he would turn into with their help, and chose "Warrior" to end the Last Great Time War once and for all. Unusually, this regeneration scene was not filmed until 2013; before that year, fans of the TV series only knew about the Eighth Doctor from the 1996 movie, before the 2005 revival jumped to a new incarnation without much explanation. Though being the "current" Doctor from 1996 to the 2005 {{revival}} in the ExpandedUniverse means that he has — and continues to have — a very healthy run, we never ''did'' know how the Paul [=McGann=] Doctor's life ''ended'', though the Time War was always the most logical assumption to make.

* John Guilor, voice imitator for the First Doctor, plays him flawlessly in some audio dramas. It's him we hear in [[Recap/DoctorWho50thASTheDayOfTheDoctor "The Day of the Doctor"]] when the First Doctor announces himself to the council.[[note]]The Time Lords, and thus the Doctor's origin, were the big reveal in the Second Doctor's final story; to those who know that, the ''First'' Doctor having anything to say about "Gallifrey" was one of the top five surprises of the episode! It also let you know ''instantly'' that this was not stock audio, but a perfect voice-over stand-in.[[/note]]

* Yet another Time Lord ([[HalfHumanHybrid or a part-Time Lord, at least]]) has been shown to have the ability — River Song, aka Mels, aka Melody Pond, daughter of Amy and Rory. This example of regeneration is particularly interesting for a number of reasons. 1) It's the first time that we meet a Time Lord's regenerations out of order (we begin with seeing River Song (Creator/AlexKingston), then we see her first body as a child (Sydney Wade), and ''then'' that body as a baby (Harrison and Madison Mortimer), and then her second body from childhood (Maya Glace-Green) to being a young adult (Nina Toussaint-White)). 2) She proved that the energy used in the regeneration can be used to heal others (a favour that the Doctor later reciprocated), so by the time of [[Recap/DoctorWhoS30E9ForestOfTheDead "Forest of the Dead"]], her third body was already decidedly her final one. 3) This unambiguously established, for the first time in a TV-continuity story, the possibility that Time Lords can RaceLift in Earth-human terms as part of a normal regeneration. 4) This is the first onscreen confirmation that non-Gallifreyans can become Time Lords, a fate originally planned for companion [[Creator/SophieAldred Ace]] but never carried out due to the cancellation of the show.

As such, the eventual "regeneration" process in "[[Recap/DoctorWhoS4E2TheTenthPlanet The Tenth Planet]]" was the writers' second intentional choice for how to change the Doctor, and it's apparent from the episode that they weren't quite sure what they'd stumbled upon. The regeneration of the First into the Second is stated to be "a feature of the TARDIS" (rather than a biological process) and [[RippedFromTheHeadlines inspired by]] [[HigherUnderstandingThroughDrugs 1960s LSD culture]] in how the experience was supposed to permanently alter his mind. The regeneration from the Second to the Third is off-screen and forced upon him by the Time Lords, and marks the first time the new Doctor was shown in his predecessor's costume. The regeneration from the Third to Fourth benefited from a Buddhist producer who [[RuleOfSymbolism made a connection with Buddhist teachings on transience and reincarnation and decided to exploit this]], and marks the point where regeneration is explicitly linked to death of the old body.

The concept of regeneration has been credited for ''Doctor Who'''s [[LongRunners long-runner status]]. As explained by showrunner Steven Moffat, the introduction of a new lead actor provides the series with an excuse to undergo a "soft reboot" or "relaunch", and indeed even when the producer and writers remain the same, the arrival of a new Doctor often results in a new feel for the show and new types of storytelling.

Every time the Doctor regenerates, the character undergoes a radical change in characterization, costume, and personality. However, all memories and past experiences of past incarnations remain, along with a certain amount of character stability (they're always going to be quirky and altruistic and fight evil aliens), meaning the Thirteenth, Tenth and Fourth Doctors are the exact same person as the First Doctor and each other, despite looking and acting much differently. Personality is a combination of "nature" and "nurture" — one story said that "Although the aspects of their personality caused by "nurture" would not change, the "nature" contribution to their personality would." The mechanic was implemented back when Creator/WilliamHartnell was playing the First Doctor, and obviously growing too ill to carry on further (plus he wasn't getting along with the current producers and in fact had nearly been fired a couple of times over the preceding year). A decision was made to let him retire and bring in Creator/PatrickTroughton for the role, and the writers decided that since the Doctor is an alien, he could change form into a new body if his current one was giving out. From there, the plot device has been modified into the go-to response for any actor wanting to depart from the role of the Doctor — kill off the current incarnation and regenerate them into the next actor, thus avoiding TheOtherDarrin (itself only invoked for the Doctor in multi-Doctor stories where an earlier incarnation's actor has already died; so far, this has only happened twice, and both times it was for the First Doctor).

Given the unique nature of ''Doctor Who'', it is one of the few (perhaps the only) productions in which different "Nth Doctors" can interact. Due to the Doctor being a Time Lord, thereby able to travel in time, the different incarnations [[MyFutureSelfAndMe interact]] from time to time, usually during [[MilestoneCelebration special anniversary storylines]]. There have also been several other characters (mostly Time Lords) who have also undergone regeneration or similar changes.

Given the unique nature of ''Doctor Who'', it is one of the few (perhaps the only) productions in which different "Nth Doctors" can interact. Due to the Doctor being a Time Lord, thereby able to travel in time, the different incarnations interact from time to time, usually during [[MilestoneCelebration special anniversary storylines]]. There have also been several other characters (mostly Time Lords) who have also undergone regeneration or similar changes.

** The Doctor's ailing health, mirroring the production difficulties caused by William Hartnell's arteriosclerosis (RealLifeWritesThePlot in action), caused his first-ever regeneration in the final moments of [[Recap/DoctorWhoS4E2TheTenthPlanet "The Tenth Planet"]].

As of 2023, the Doctor has been played (as the lead role, see notes below) canonically by fifteen actors. Note that the canonical "numbering" of the Doctors does not match up with the number of times the Doctor has regenerated. This is because the War Doctor was {{retcon}}ned into the cycle situated between Eight and Nine especially for the [[http://en.wikipedia.org/wiki/The_Day_of_the_Doctor#Broadcast 50th Anniversary]], and the Tenth Doctor managed to regenerate twice by cheating the system. Interestingly enough, Fourteen is also played by David Tennant and thus shares the same face as Ten, but qualifies as a separate incarnation.\\\

-->-- '''The Ninth Doctor''', explaining regeneration to Rose Tyler, "[[Recap/DoctorWhoS27E13ThePartingOfTheWays The Parting of the Ways]]"

As of 2023, the Doctor has been played (as the lead role, see notes below) canonically by fifteen actors. Note that the canonical "numbering" of the Doctors does not match up with the number of times the Doctor has regenerated. This is because the War Doctor was {{retcon}}ned into the cycle situated between Eight and Nine especially for the [[http://en.wikipedia.org/wiki/The_Day_of_the_Doctor#Broadcast 50th Anniversary]], and the Tenth Doctor managed to regenerate twice by cheating the system. Interestingly enough, Fourteen is also played by David Tennant and thus shares the same face as Ten, but qualifies as a separate incarnation.

* Creator/WilliamHartnell (First Doctor, 1963-1966)

* Creator/PatrickTroughton (Second Doctor, 1966-1969)

* Creator/JonPertwee (Third Doctor, 1970-1974)

* Creator/TomBaker (Fourth Doctor, 1974-1981)

* Creator/PeterDavison (Fifth Doctor, 1981-1984)

* Creator/ColinBaker (Sixth Doctor, 1984-1986)

* Creator/SylvesterMcCoy (Seventh Doctor, 1987-1989 and 1996 TV Movie)

* Creator/PaulMcGann (Eighth Doctor, 1996 TV Movie and 2013 Anniversary short)

* Creator/JohnHurt (War Doctor, 2013; introduced in [[Recap/DoctorWhoS33E13TheNameOfTheDoctor "The Name of the Doctor"]], retroactively debuted in [[Recap/DoctorWho50thPrequelTheNightOfTheDoctor "The Night of the Doctor"]], and appeared in [[Recap/DoctorWho50thASTheDayOfTheDoctor "The Day of the Doctor"]])
** Regenerated into the Ninth Doctor at the end of [[Recap/DoctorWho50thASTheDayOfTheDoctor "The Day of the Doctor"]] due to apparent old age and fatigue; this regeneration worked more like a system update, and didn't really seem to cause any form of agony or difficulty for him (although the Ninth Doctor's actions immediately after the change have yet to be depicted on screen, the events of [[RRecap/DoctorWhoS27E1Rose "Rose"]] came very soon after this regeneration). This incarnation did not use the name "Doctor" until the end of his life, thus he is not counted as a numbered Doctor either in or out of universe.
* Creator/ChristopherEccleston (Ninth Doctor, 2005)

* Creator/DavidTennant (Tenth Doctor, 2005-2010); this Doctor regenerated ''twice''.

* Creator/MattSmith (Eleventh Doctor, 2010-2013)

* Creator/PeterCapaldi (Twelfth Doctor, 2013-2017)

* Creator/JodieWhittaker (Thirteenth Doctor, 2017-2022)

* David Tennant (Fourteenth Doctor, 2022-2023)

* Creator/NcutiGatwa (Fifteenth Doctor, starting in 2023)
** The first main black incarnation of the Doctor; Creator/ColinSalmon's Doctor Moon was a minor character who was only confirmed to be the Doctor via WordOfGod, while Creator/JoMartin's Fugitive is outside of the main sequence.

As of 2023, the Doctor has been played (as the lead role, see notes below) canonically by fifteen actors. Note that the canonical "numbering" of the Doctors does not match up with the number of times the Doctor has regenerated. This is because the War Doctor was {{retcon}}ned into the cycle situated between Eight and Nine especially for the [[http://en.wikipedia.org/wiki/The_Day_of_the_Doctor#Broadcast 50th Anniversary]], and David Tennant portrayed three regenerations, as Ten regenerated into himself on one occasion and Fourteen shares the same face as Ten.

As of 2017, the Doctor has been played (as the lead role, see notes below) canonically by thirteen actors. Note that the canonical "numbering" of the Doctors does not match up with the number of times the Doctor has regenerated. This is because the War Doctor was {{retcon}}ned into the cycle situated between Eight and Nine especially for the [[http://en.wikipedia.org/wiki/The_Day_of_the_Doctor#Broadcast 50th Anniversary]], and David Tennant portrayed two regenerations as Ten regenerated into himself on one occasion.

** Regenerated into the Ninth Doctor at the end of [[Recap/DoctorWho50thASTheDayOfTheDoctor "The Day of the Doctor"]] due to apparent old age and fatigue; this regeneration worked more like a system update, and didn't really seem to cause any form of agony or difficulty for him (although the Ninth Doctor's actions immediately after the change have yet to be depicted on screen, the events of [[Recap/DoctorWhoNSS1E1Rose "Rose"]] came very soon after this regeneration). This incarnation did not use the name "Doctor" until the end of his life, thus he is not counted as a numbered Doctor either in or out of universe.

Given the unique nature of ''Doctor Who'', it is one of the few (perhaps the only) productions in which different "Nth Doctors" can interact. Due to the Doctor being a Time Lord, thereby able to travel in time, the different incarnations interact from time to time, usually during [[MilestoneEpisode special anniversary storylines]]. There have also been several other characters (mostly Time Lords) who have also undergone regeneration or similar changes.

The concept of regeneration has been credited for ''Doctor Who''[='s=] [[LongRunners long-runner status]]. As explained by showrunner Steven Moffat, the introduction of a new lead actor provides the series with an excuse to undergo a "soft reboot" or "relaunch", and indeed even when the producer and writers remain the same, the arrival of a new Doctor often results in a new feel for the show and new types of storytelling.

As such, the eventual "regeneration" process in [[Recap/DoctorWhoS4E2TheTenthPlanet "The Tenth Planet"]] was the writers' second intentional choice for how to change the Doctor, and it's apparent from the episode that they weren't quite sure what they'd stumbled upon. The regeneration of the First into the Second is stated to be "a feature of the TARDIS" (rather than a biological process) and [[RippedFromTheHeadlines inspired by]] [[HigherUnderstandingThroughDrugs 1960s LSD culture]] in how the experience was supposed to permanently alter his mind. The regeneration from the Second to the Third is off-screen and forced upon him by the Time Lords, and marks the first time the new Doctor was shown in his predecessor's costume. The regeneration from the Third to Fourth benefited from a Buddhist producer who [[RuleOfSymbolism made a connection with Buddhist teachings on transience and reincarnation and decided to exploit this]], and marks the point where regeneration is explicitly linked to death of the old body.

Given the unique nature of ''Doctor Who'', it is one of the few (perhaps the only) productions in which different "Nth Doctors" can interact. Due to the Doctor being a Time Lord, thereby able to travel in time, the different incarnations interact from time to time, usually during special anniversary storylines. There have also been several other characters (mostly Time Lords) who have also undergone regeneration or similar changes.

* The 1976 Fourth Doctor serial "[[Recap/DoctorWhoS13E5TheBrainOfMorbius The Brain of Morbius]]" suggested that the Doctor had at least eight different incarnations before the First Doctor. This was largely ignored by the fandom, who accepted the twelve-regeneration limit and the First Doctor as the original incarnation of the Doctor, and later informally retconned them into being previous incarnations of Morbius, but "The Timeless Children" forced the episode back into public consciousness by [[spoiler:confirming that they are the unseen incarnations of the Timeless Child, who eventually becomes the Doctor.]] The faces representing these incarnations are actually mugshots of various men on the story's production team[[note]]from top-left of [[https://static.wikia.nocookie.net/tardis/images/b/b9/Morbius_Doctors_bigger.JPG this image]]: Christopher Barry, Robert Banks Stewart, Christopher Baker, Creator/PhilipHinchcliffe, Douglas Camfield, Graeme Harper, Martin Jurgens, and George Gallaccio[[/note]], and they technically never portrayed the Doctor in any media, but producer Creator/PhilipHinchcliffe fully intended to make the "Morbius Doctors" canon.

* It also wasn't the last time they did it either — ''The Trouble with Drax'' features Ray Brooks as the third incarnation of wheeler-dealer Drax, taking over for the deceased Barry Jackson, who's established as having been Drax's second incarnation. [[spoiler:A number of supporting characters in the story also turn out to be incarnations of Drax, with John Challis as the fifth, Miranda Raison as the eighth, Creator/JohnLeeson as the ninth, and Hugh Fraser as the twelfth.]]

* The non-dramatic parts of the Expanded Universe have introduced a few versions of regenerated Time Lord characters who were never played by any real actor. The ''Literature/DoctorWhoNewAdventures'' featured a new version of the Master [[ComicBookFantasyCasting physically based]] on Creator/BasilRathbone, the ''Literature/EighthDoctorAdventures'' introduced an antagonistic third incarnation of Romana physically based on Louise Brooks, the ''Literature/PastDoctorAdventures'' had a brief appearance from a dark-skinned future incarnation of Romana in [[spoiler:''Tomb of Valdemar'']], the ''Literature/DoctorWhoNovelisations'' had the Doctor's Merlin incarnation feature in the ''Battlefield'' novelisation's prologue, a man with unruly red hair, a tatty embroidered Afghan coat, and a floppy brown felt hat with a bandana around the brim, and the novelisation of ''Rose'' had Clive show Rose two original incarnations of the Doctor on top of the official ones, one a tall, bald black woman, the other an [[AmbiguousGender androgynous]] child in a hi-tech wheelchair with a robot dog, the ''Magazine/DoctorWhoMagazine'' comic strips featured a unique version of the Master during the Eighth Doctor's era, who was black in human ethnic terms, and featured an incarnation of Rassilon preceding all those on-screen, an older dark-skinned woman, for their tie-in to the ''Time Lord Victorious'' multi-platform event, "Monstrous Beauty", and the ''ComicBook/DoctorWhoTitan'' Eleventh Doctor comics featured an East-Asian-looking boy War Master who accompanied the War Doctor for a time during the Time War, and has occasionally made appearances in other Titan comics.

** The Doctor's first female incarnation in the TV series, building off the cross-gender regenerations shown during the Twelfth Doctor's era.

** The first Doctor to be played by the same actor as another incarnation, with the Thirteenth Doctor having mysteriously regenerated into this familiar form at the end of "The Power of the Doctor". Tennant will star in three specials in November 2023 to commemorate the show’s 60th anniversary, before regenerating into the Fifteenth Doctor.

** Played the Master for a single scene in [[Recap/DoctorWhoTVMTheTVMovie the TV Movie]], seen only from behind and from the neck down. This may or may not be the same incarnation as Ainley's Master.

** No regeneration scene was filmed, but this Master "died" at the end of his only appearance.

** Played a Master who has been saved from his {{Body Surf}}ing predicament by having been granted a new regeneration cycle by the Time Lords, of which it is strongly implied that he is the first new incarnation. He is further implied to have been the Master who fought in the Time War.

** This Master was disguised as a man named "Professor Yana" under the effects of a Chameleon Arch.
** Jacobi also portrayed a mostly-reformed Master in "Scream of the Shalka", though it was a different situation from Yana's.

** Was apparently unable to regenerate after being shot in the back by the Saxon Master ([[HeelFaceDoorSlam who wanted to prevent her from helping the Doctor]]).

** Originally known as "O", revealed as the Master at the end of his first episode, part 1 of [[Recap/DoctorWhoS38E1E2Spyfall "Spyfall"]].

* Borusa, a senior Time Lord on Gallifrey and the Doctor's old Academy tutor, was in a different regeneration in each of the four stories he appeared in, being played by Angus [=MacKay=] in [[Recap/DoctorWhoS14E3TheDeadlyAssassin "The Deadly Assassin"]], John Arnatt in [[Recap/DoctorWhoS15E6TheInvasionOfTime "The Invasion of Time"]], Leonard Sachs in [[Recap/DoctorWhoS20E1ArcOfInfinity "Arc of Infinity"]] and Philip Latham in [[Recap/DoctorWho20thASTheFiveDoctors "The Five Doctors"]]. No explanation was given for the rapidity of his regenerations, although many fans like to take it as an indication of [[KlingonPromotion how Time Lord politics work]]. This became something of an in-joke in the expanded universe: in the War Doctor prose novel ''[[Recap/NewSeriesAdventuresEnginesOfWar Engines of War]]'', Borusa is shown in several different regenerations, including a middle-aged woman — possibly a sneaky reference to an AlternateUniverse Borusa seen in the ''AudioPlay/{{Gallifrey}}'' series (on an alternate version of the planet), in which she was played by Creator/KatyManning. The version of Borusa who actually taught the Doctor at the Academy appears briefly in a flashback in the Tenth Doctor ''ComicBook/DoctorWhoTitan'' comics, and is depicted as a stout, elderly, bearded black man.

* K9's voice actor changed in Season 17 from Creator/JohnLeeson, the person most associated with the role (he's still voicing the character to this day), to Creator/DavidBrierly. This was explained on-screen by K9 having "robot laryngitis" during the first story of Season 17 (and thus not having to speak or take part) and the Doctor not quite repairing him correctly until the next season. In-verse, the Doctor left K9 with companions who were parting company with him on a couple of occasions, unpacking a new copy of the robot dog for himself each time. Presumably he downloaded the previous K9's memories and personality into the new housing to ensure it remained "his" dog. A heavily-modified version of K9 also featured in the spinoff ''Series/{{K9}}''.

** ''VideoGame/LegoDimensions'' also uses this game mechanic for the Doctor. All main Doctors up to the Twelfth, plus John Hurt's War Doctor, can be played. It happens whenever the "current" version of the Doctor is killed.

** ''The Mazes of Time'' has the Eleventh Doctor "regenerate" but staying in the same body whenever he is killed. Even Amy Pond, his human companion, can regenerate here. Figure that one out.

Every time the Doctor regenerates, the character undergoes a radical change in characterization, costume, and personality. However, all memories and past experiences of past incarnations remain, along with a certain amount of character stability (they're always going to be quirky and altruistic and fight evil aliens), meaning the Thirteenth Doctor, the Tenth Doctor and the Fourth Doctor are the exact same person as the First Doctor despite looking and acting much differently. Personality is a combination of "nature" and "nurture" — one story said that "Although the aspects of their personality caused by "nurture" would not change, the "nature" contribution to their personality would." The mechanic was implemented back when Creator/WilliamHartnell was playing the First Doctor, and obviously growing too ill to carry on further (plus he wasn't getting along with the current producers and in fact had nearly been fired a couple of times over the preceding year). A decision was made to let him retire and bring in Creator/PatrickTroughton for the role, and the writers decided that since the Doctor is an alien, he could change form into a new body if his current one was giving out. From there, the plot device has been modified into the go-to response for any actor wanting to depart from the role of the Doctor — kill off the current incarnation and regenerate them into the next actor, thus avoiding TheOtherDarrin (itself only invoked for the Doctor in multi-Doctor stories where an earlier incarnation's actor has already died; so far, this has only happened twice, and both times it was for the First Doctor).

Every time the Doctor regenerates, the character undergoes a radical change in characterization, costume, and personality. However, all memories and past experiences of past incarnations remain, along with a certain amount of character stability (they're always going to be quirky and altruistic and fight evil aliens), meaning the Thirteenth Doctor is the exact same person as the First Doctor. Personality is a combination of "nature" and "nurture" — one story said that "Although the aspects of their personality caused by "nurture" would not change, the "nature" contribution to their personality would." The mechanic was implemented back when Creator/WilliamHartnell was playing the First Doctor, and obviously growing too ill to carry on further (plus he wasn't getting along with the current producers and in fact had nearly been fired a couple of times over the preceding year). A decision was made to let him retire and bring in Creator/PatrickTroughton for the role, and the writers decided that since the Doctor is an alien, he could change form into a new body if his current one was giving out. From there, the plot device has been modified into the go-to response for any actor wanting to depart from the role of the Doctor — kill off the current incarnation and regenerate them into the next actor, thus avoiding TheOtherDarrin (itself only invoked for the Doctor in multi-Doctor stories where an earlier incarnation's actor has already died; so far, this has only happened twice, and both times it was for the First Doctor).

** First known as "Missy", revealed as the Master at the end of the Twelfth Doctor's first season.