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"Time Lords have this little trick. It's sort of a way of cheating death, except... it means I'm gonna change. And I'm not gonna see you again. Not like this, not with this daft old face."
The Ninth Doctor, explaining regeneration to Rose Tyler, "The Parting of the Ways"

This is the page for The Nth Doctor in its trope-naming and trope-codifying franchise.

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 William Hartnell 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 Patrick Troughton 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, never invoking The Other Darrin.


During the tenure of the First Doctor, observant viewers can note various plot developments involving the Doctor's consciousness being placed into the body of someone else — not all of which, strangely enough, were intended to write William Hartnell out permanently. "The Celestial Toymaker", which has the Doctor phased out of existence for most of the story, was supposed to end with the Doctor being phased back into existence but in a different body, as there was strong pressure on Hartnell to quit around that time. "The Savages", which shows the Doctor having his life force drained from him, and then using a Batman Gambit and a Soul Fragment to place his personality into a Noble Demon villain, wasn't intended as a way to replace Hartnell, since his contract wasn't up yet, but as a way to give him some time to work on another storynote .


As such, the eventual "regeneration" process in "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 inspired by 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 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 concept of regeneration has been credited for Doctor Who's 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.

In the words of River Song — spoilers!

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    The Doctor 
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 retconned into the cycle situated between Eight and Nine especially for the 50th Anniversary, and David Tennant portrayed two regenerations as Ten regenerated into himself on one occasion.

The following actors have portrayed the Doctor:

  • William Hartnell (First Doctor, 1963-1966)
    • The Doctor's ailing health, mirroring the production difficulties caused by William Hartnell's arteriosclerosis (Real Life Writes the Plot in action), caused his first-ever regeneration in the final moments of "The Tenth Planet".
  • Patrick Troughton (Second Doctor, 1966-1969)
    • Regenerated off-screen as a punishment after the Time Lords found him guilty of stealing the TARDIS and breaking the law of non-interference between "The War Games" and "Spearhead from Space"; the actual process of his regeneration was depicted in the comic strip, "The Night Walkers".note 
  • Jon Pertwee (Third Doctor, 1970-1974)
    • Regenerated due to radiation poisoning caused by the caves of Metabelis III in "Planet of the Spiders"; amazingly, the Doctor was able to go on for three years (in in-universe time, not real time), lost in the Time Vortex, before regenerating.
  • Tom Baker (Fourth Doctor, 1974-1981)
    • Regenerated after suffering a long drop off of the Pharos Project radio telescope in "Logopolis"; this regeneration required help from the Watcher (a one-off "in-between" entity that has never been seen since), and the result was so difficult a regeneration that the Doctor was forced to put himself in stasis for some time in "Castrovalva".
    • Tom Baker also portrayed the Curator, an ambiguous figure who might be a future Doctor, in "The Day of the Doctor" in 2013.note 
  • Peter Davison (Fifth Doctor, 1981-1984)
    • Regenerated due to contracting Spectrox Toxemia (caused by exposure to raw spectrox) in the Spectrox Mines of Androzani Minor in the first scenes of "The Caves of Androzani". His regeneration was at the end of the serial, and was only necessary due to... a long story. Basically, he and Peri both contracted poisoning, the Doctor spent a good deal of the episode trying to get milk from a Queen Bat (as the milk was the only known cure for the condition), and when he finally did get enough milk for Peri and him, one of the vials spilled open. The Doctor chose to give the remaining vial to Peri, and was forced to regenerate in the most spectacular fashion ever achieved in the classic series. However, the resulting change left the Doctor unstable, leading to him attacking Peri soon after the change, which led to him becoming The Atoner for the rest of the story.
  • Colin Baker (Sixth Doctor, 1984-1986)
    • Regenerated in The Teaser of "Time and the Rani", due to unknown injuries received beforehand. There's a lot of official Fix Fic about that one, the most notable one being in Big Finish Doctor Who's 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 Heroic Suicide due to... another long story: The Valeyard (see below) has hatched an Assimilation Plot 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 Real Life Writes the Plot 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 Fake Shemp Sylvester McCoy as the Sixth Doctor briefly.
  • Sylvester McCoy (Seventh Doctor, 1987-1989 and 1996 TV Movie)
    • Yet another long story: in 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 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 Never Live It Down 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.
  • Paul McGann (Eighth Doctor, 1996 TV Movie and 2013 Anniversary short)
    • The circumstances of his death long unrevealed, we learn in a DVD short called "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 Expanded Universe 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 Hurt (War Doctor, 2013; introduced in "The Name of the Doctor", retroactively debuted in "The Night of the Doctor", and appeared in "The Day of the Doctor")
    • Regenerated into the Ninth Doctor at the end of "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 "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.
  • Christopher Eccleston (Ninth Doctor, 2005)
    • Regenerated due to cellular degeneration caused by absorbing the entire Time Vortex from Rose in order to save her life, in "The Parting of the Ways".
  • David Tennant (Tenth Doctor, 2005-2010); this Doctor regenerated twice.
    • His first regeneration occurred after being shot by a Dalek at the end of "The Stolen Earth", but redirected the regenerative energy that would've changed his appearance into his severed hand (which later grew into a new Doctor) from "The Christmas Invasion" because he "had vanity issues at the time." (He also doesn't suffer from any post-regenerative trauma after this regeneration, but this is never explicitly stated as the reason he did it.) As a result, the regeneration was aborted without changing his appearance.
    • His second regeneration, this time a complete one, occurred after absorbing a massive dose of radiation in Wilf's stead in "The End of Time". Since he took the time to hold back his regeneration and say goodbye to the Russell T Davies era of companions, this Doctor's regeneration was powerful enough to wreck the TARDIS interior, causing her to shut down for repair in "The Eleventh Hour".
    • David Tennant also portrayed the Meta-Crisis Tenth Doctor, a half-human clone of the Tenth Doctor created by the aftermath of the aforementioned sidestepped regeneration, in the 2008 episode "Journey's End". Following his first aborted regeneration, companion Donna Noble interacted with the hand while it was infused with live regeneration energies. It sampled her DNA and used it to fashion a whole new body for the hand, creating a clone of the Tenth Doctor that looked just like him, but had one heart, no regenerations, a human lifespan, some of Donna's temper, and an apparently more unhinged personality.
  • Matt Smith (Eleventh Doctor, 2010-2013)
    • Regenerated due to old age in "The Time of the Doctor". This Doctor was supposed to die (as he had used up all 12 of his allowed regenerations), but thanks to a plea by his companion, Clara, the Time Lords granted him a brand-new cycle at the last minute to allow him to save Gallifrey. (This involved rewriting history in which the Doctor's death was already established fact; consequences of this reverberated throughout the 11th Doctor's incarnation.)
  • Peter Capaldi (Twelfth Doctor, 2013-2017)
    • Now that people had been reintroduced to Doctor Who, they could be reintroduced to the idea that the Doctor could be played by any man, not just young ones. One character even commented that the two previous Doctors had been "flirting with the entire universe" with their youthful looks and normally cheerful demeanor, and challenged his companion Clara Oswald to not give up on him now that he was a crotchety Scotsman. Not only did she not give up, by the end of her time with him, despite their age difference, they had entered into a form of old-fashioned romance. It should be noted that though his last moments were in his youthful form, the Eleventh Doctor aged considerably offscreen in his last episode, presumably so an older Doctor made narrative sense.
    • "The Lie of the Land" had the Doctor demonstrate he could fake a regeneration, simulating its effects without going through with it, doing so as part of a Secret Test of Character for Bill.
    • Started to regenerate for real in The Teaser of "World Enough and Time", before the story jumped back to show the events leading up to it, eventually turning out in "The Doctor Falls" to have begun after the Doctor was electrocuted by a Cyberman. However, he repeatedly held the regeneration off, not wanting to change again, despite taking repeated injuries while fighting against the Cybermen. The Doctor's refusal to change was such that at one point, after blowing up a Cyber-army, he chose to die rather than regenerate, but was saved by companion Bill Potts, who inadvertently brought him back to life, although still on the verge of regeneration. The story ended with the "World Enough and Time" scene, but again the Doctor held off regenerating, finally going through with it in "Twice Upon a Time" where he was convinced to regenerate in order to continue saving lives. Like the Tenth Doctor's regeneration into the Eleventh, the built-up regeneration energy resulting from the delay caused serious damage to the TARDIS, resulting in the Thirteenth Doctor being thrown out of and separated from her.
  • Jodie Whittaker (Thirteenth Doctor, 2017-present)
    • The Doctor's first female incarnation in the TV series, building off the cross-gender regenerations shown during the Twelfth Doctor's era.
  • Ncuti Gatwa (Fourteenth Doctor, starting in 2023)
    • The first main black incarnation of the Doctor, Jo Martin's Fugitive having been part of Thirteenth's cast.

In addition, the following actors have been cast as "The Doctor", but have not actually portrayed the role as the original Doctor, but as a stand-in for an unavailable or deceased actor, an Affectionate Parody, a Docudrama, or an alternate version of the Doctor altogether:
  • Edmund Warwick as a "Robot Dr. Who" in the 1965 story "The Chase".
  • Peter Cushing as a human named Dr. Who in the 1966 film, Dr. Who and the Daleks and its 1967 sequel, Daleks' Invasion Earth: 2150 A.D.. The films were adaptations and reimaginings of TV stories, with a number of key elements changed, such as the Doctor's character.
  • Trevor Martin as an alternate Fourth Doctor for the 1974 stage play Doctor Who and the Seven Keys to Doomsday. Tom Baker had yet to be cast as the official Fourth Doctor. The Third Doctor "regenerated" onstage and Martin took over during the play.note 
  • The 1976 Fourth Doctor serial "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 retconned into them being previous incarnations of Morbius, but "The Timeless Children" forced the episode back into public consciousness by 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 teamnote , and they technically never portrayed the Doctor in any media, but producer Philip Hinchcliffe fully intended to make the "Morbius Doctors" canon.
  • Adrian Gibbs as the Watcher, a ghostly manifestation of the regeneration halfway completed from the Fourth to Fifth Doctors in the 1981 story, "Logopolis". His origins were vaguely explained at best, and he vanished after merging with the Fourth Doctor to regenerate him into the Fifth Doctor.
  • Richard Hurndall, cast as the First Doctor in the 1983 20th anniversary special "The Five Doctors", as William Hartnell had died by this point.
  • Lenny Henry in a 1985 comic sketch as an alternate Seventh Doctor post-regeneration, facing off against the evil Cyberman "Thatchos".
  • Michael Jayston as the Valeyard, allegedly a potential evil future incarnation of the Doctor or undesired side effect born out of the Doctor, in 1986's The Trial of a Time Lord (Season 23) and some spin-off Big Finish media.
  • As noted above, Sylvester McCoy was required to Fake Shemp for the Sixth Doctor during the regeneration sequence in "Time and the Rani".
  • David Banks as an alternate Doctor and Jon Pertwee's understudy in the 1989 stage play Doctor Who: The Ultimate Adventure when Pertwee had fallen ill and could not perform onstage.
  • Rowan Atkinson, Richard E. Grant, Jim Broadbent, Hugh Grant, and Joanna Lumley as alternate Ninth through Thirteenth Doctors in the parodic BBC Red Nose Day special of 1999, The Curse of Fatal Death, regenerating for humourous and rather absurd reasons.
  • Mark Gatiss as an unnumbered Doctor in the 1999 spoof "The Web of Caves".
  • Richard E. Grant again, this time as the Shalka Doctor for the 2003 web release Scream of the Shalka, who was intended as the official Ninth Doctor but was removed from continuity following the BBC Wales-produced revival of the series with Eccleston.
  • The Alternate Universe Big Finish portrayals:
    • Geoffrey Bayldon as an alternate First Doctor who never left Gallifrey.
    • David Warner as an alternate Third Doctor who arrived on Earth for his exile years after he did in mainstream canon, leading to everything on Earth utterly going to Hell.
    • David Collings as a less sympathetic alternate Future Doctor.
    • Michael Jayston as an alternate Valeyard who became the Doctor.
    • Arabella Weir as an alternate and comical female Third Doctor.
    • Colin Baker as an alternate War Doctor known as "the Warrior" who came into being earlier in the Doctor's timeline than mainstream canon, in a universe where the Fourth Doctor decided to destroy the Daleks in "Genesis of the Daleks".
  • Jon Culshaw as a stand-in for Tom Baker, due to his uncanny impersonation of the actor's voice. Periodically cast in Big Finish audios, and also played the "real life" Tom Baker in a 50th anniversary spoof.
  • Toby Jones as the Dream Lord, a malicious manifestation of the Doctor's self-loathing, in the 2010 episode "Amy's Choice".
  • Daniel Anthony, who played Clyde Langer in The Sarah Jane Adventures, briefly played the Eleventh Doctor in Clyde's body thanks to a mishap in the 2010 SJA serial "Death of the Doctor".
  • David Bradley (portrayed William Hartnell and Hartnell in-character as the First Doctor) in the 2013 docudrama An Adventure in Space and Time. He reprised the role within the show's canon for the 2017 Christmas Special, "Twice Upon a Time", and has subsequently voiced the First Doctor in Big Finish audios.
  • Tony Garner as the "Second-and-a-Half" Doctor in the fan-production Devious. Created when the Second Doctor's regeneration is delayed during the stay of his sentencing, and later completes his transformation into the Third Doctor once the sentence is ultimately completed. The production has been in Development Hell since 1995, but did star Jon Pertwee in one of his final performances as the Third Doctor.
  • An uncredited child actor appeared as a very young First Doctor in the Series 8 episode "Listen". Only the child-Doctor's feet, ankles, hair and silhouette are shown on screen, to leave the young Doctor's appearance to viewers' imagination, although he does speak a line.
  • Uncredited body doubles Fake Shemp for past versions of the Doctor in "The Name of the Doctor" (with archive footage of the original actors also used) and "The Witch's Familiar".
  • Tim Treloar, who was cast as the voice of the Third Doctor in the Big Finish audios in place of the late Jon Pertwee.
  • John Guilor, voice imitator for the First Doctor, plays him flawlessly in some audio dramas. It's him we hear in "The Day of the Doctor" when the First Doctor announces himself to the council.note 
  • William Russell, who played day-one companion Ian Chesterton in the classic series, voices the First Doctor in a number of Big Finish audios.
  • Frazer Hines, who played companion Jamie McCrimmon in the classic series, voiced the Second Doctor in the Big Finish audio "The Light at the End".
  • Patrick Troughton's sound-a-like son, David, has also portrayed his father's Doctor in a few audio dramas.
  • "Fugitive of the Judoon" introduces Jo Martin as an incarnation of the Doctor whose position in the timeline is unknown, as neither she nor Thirteen remember ever being each other. She's also the first-ever non-white incarnation of the Doctor. After the events of "The Timeless Children", she's likely a past incarnation who worked for the Division.
  • "The Timeless Children" has every single actor who plays the Timeless Child. It's revealed the Doctor is much, much older than they ever knew and has had countless lives that they've been made to forget since they started as the Timeless Child. Several of these lives, encompassing a wide variety of appearances, make brief appearances throughout the episode.
  • Jonathon Carley, who was cast as the voice of a younger War Doctor in the Big Finish audios following John Hurt's death.
  • Patrick Troughton's other actor son, Michael, has been cast as the voice of his father's Doctor in the Big Finish audios as well.
  • Stephen Noonan voices the First Doctor in some Big Finish audios.

    The Master 
Though he's been shown to explicitly regenerate only once onscreen (two other times, he's just stolen bodies of other people), fourteen people have played the Master so far.
  • Roger Delgado (1971-1973)
    • The actor died before a death scene could be filmed; the writers' intent was for the Master to die saving the Doctor in a Heroic Sacrifice. The Master's subsequent change of appearance was later explained in the Eighth Doctor Adventures novel Legacy of the Daleks where he was shot with his own weapon by Susan Foreman, who then stole his TARDIS; this was not a regeneration, as the Master had already regenerated twelve times by this point. An entirely different demise for the Delgado Master was later depicted in the Twelfth Doctor Doctor Who Magazine comic strip story "Doorway to Hell", in which he was blasted with an energy bolt by the Doctor's temporarily empowered companion and her family (long story, it was after a lot of provocation), and was then depicted as attempting to regenerate in the usual manner, which presumably failed and turned him into the rotting Pratt form, unless one considers Big Finish audios to be canon. In "The Two Masters", the Pratt/Beevers incarnation originally had a fully healthy body, but was severely injured by the Macqueen incarnation, as part of the Macqueen Master's plan to fake the death of his earlier incarnation, in order to gain access to a cult that had instructed him to kill one of his past selves.
  • Peter Pratt (1976)
    • Played the decayed form of the Master in "The Deadly Assassin", unable to regenerate as he is "at the end of his final regeneration". If one takes the books as canon, this is the same incarnation as Delgado.
  • Geoffrey Beevers (1981; same incarnation as Pratt)
    • Played the decayed form of the Master in "The Keeper of Traken"; this was the same role previously played by Pratt, making the Master one of the few characters to have been both an Nth Doctor and an Other Darrin. The Big Finish story "Trail of the White Worm" did have an explanation for his different appearance compared to the Pratt Master; he is a somewhat healthier and stabler version, having used energy from the Eye of Harmony to heal himself. Beevers also (technically) voiced Eric Roberts' Master in the Big Finish audios.
    • Changed appearance — again without regenerating — in "The Keeper of Traken" by stealing the body of the significantly named Tremas.
  • Anthony Ainley (1981-1989)
    • Played the Master from the end of the Tom Baker era all the way to the end of the classic series.
    • No regeneration scene was filmed, as the character was recast for the TV Movie.
  • Gordon Tipple (1996)
    • Played the Master for a single scene in 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.
    • After being exterminated by the Daleks, the Master took over the body of an ambulance driver named Bruce.
  • Eric Roberts (1996)
    • Played the Master's new body-hop victim Bruce, and thus was the Master himself for most of the film.
    • No regeneration scene was filmed, but this Master "died" at the end of his only appearance.
  • Alex Macqueen (various Big Finish audios)
    • Played a Master who has been saved from his Body Surfing 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.
  • Derek Jacobi (2007)
    • 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.
    • Regenerated after being shot by his (or rather, Yana's) assistant Chantho. This is the only time a regeneration of the Master has been depicted onscreen.
  • John Simm (2007-2010, 2017)
    • Used the civilian identity of "Harold Saxon", and became Prime Minister.
    • Died in "Last of the Time Lords" after being shot by his wife, and refused to regenerate. Later revived by a cult in "The End of Time", but died again in a Heroic Sacrifice, or so it appeared at the time. The episode suggests that the Master considered his revived form to be a new incarnation who happens to look the same as his last one.
    • Reappeared alongside Missy in Series 10. From his perspective, it's sometime after the events of "The End of Time".
    • Was stabbed in the back by his future incarnation Missy (whom he shot with his laser screwdriver shortly afterwards), and is implied to have later regenerated into her offscreen.
  • Michelle Gomez (2014-2017)
  • Sacha Dhawan (2020-)
    • Originally known as "O", revealed as the Master at the end of his first episode, part 1 of "Spyfall".
    • The Master's first onscreen non-white incarnation.

  • William Hughes (2007), a child actor, played the 8-year-old Master in a flashback in "The Sound of Drums". Hughes' unspeaking role is the only time the character's original appearance has been portrayed on-screen.
  • Exclusive to Titan Comics is a wartime Master who appears in the form of an "Asian child". Working alongside the War Doctor, this Master demonstrates how timey-wimey the Time War is by his brief and spontaneous transformation into a past Master, namely Delgado. Ultimately, this incarnation regenerates into the Jacobi Master.
  • James Dreyfus played an earlier, pre-Delgado incarnation of the Master, contemporary to the First and Second Doctors in Big Finish audio dramas.
  • Gina McKee played the Lumiat in the Big Finish story of the same name. Following Missy, who cheated death thanks to a hidden gadget, the Lumiat inherited her predecessor's Heel–Face Turn and strove to be a force for good, becoming the Master's equivalent of the Valeyard. Ultimately, she ran afoul of and was mortally wounded by a younger, pre-Heel–Face Turn Missy, resulting in her regeneration into what Word of God confirms is the Dhawan Master.

  • A temporary case of this trope occurred in "The Mind Robber". Frazer Hines got chicken pox, and was replaced for one episode by Hamish Wilson. Fortunately, that serial is something of a Mind Screw, so they were able to provide a "sensible" explanation: Jamie is reduced to a "puzzle" that the Doctor must solve by picking the right facial features. He does so incorrectly and gives Jamie the wrong face. Later on it happens again, and he is able to fix his mistake. Makes about as much sense as anything else that happens in that story.
  • Romana regenerated from Mary Tamm into Lalla Ward — who, confusingly enough, had appeared alongside Tamm in a serial just before she took over the role. This got explained by Romana liking Princess Astra's appearance so much that she decided to regenerate into a double of her. During the regeneration sequence, several uncredited actresses portrays "in-between" versions of Romana as she tries out different bodies, something not portrayed on screen since. A third Romana, played by Juliet Landau, was introduced in the EU audio dramas in 2013; she is said to be a future incarnation, possibly from thousands of years into the future, so it's not known how many Romanas existed before her.
  • 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 "The Deadly Assassin", John Arnatt in "The Invasion of Time", Leonard Sachs in "Arc of Infinity" and Philip Latham in "The Five Doctors". No explanation was given for the rapidity of his regenerations, although many fans like to take it as an indication of how Time Lord politics work. This became something of an in-joke in the expanded universe: in the War Doctor prose novel Engines of War, Borusa is shown in several different regenerations, including a middle-aged woman — possibly a sneaky reference to an Alternate Universe Borusa seen in the Gallifrey series (on an alternate version of the planet), in which she was played by Katy Manning. The version of Borusa who actually taught the Doctor at the Academy appears briefly in a flashback in the Tenth Doctor Doctor Who (Titan) comics, and is depicted as a stout, elderly, bearded black man.
  • The first on-screen regeneration of a Time Lord other than the Doctor occurs in "Planet of the Spiders", when K'anpo Rimpoche (aka the Hermit, the Doctor's childhood spiritual advisor who'd travelled to Earth and adopted the identity of a Tibetan abbot) is fatally wounded by his EightLegs-dominated students. Upon regenerating, he assumes the form of Cho-Je, his supposed assistant: actually a projection of his own self, and perhaps a more expertly-produced and consciously-controlled equivalent of the Watcher (see above).
  • Rassilon, the ruthless and egomaniacal founder of Time Lord society, has been played by five actors: Richard Mathews in "The Five Doctors", Timothy Dalton in "The End of Time" and Donald Sumpter in "Hell Bent", while Big Finish adds both Don Warrington and Richard Armitage to the mix, chronologically following Mathews but preceeding Dalton.
  • In "The Hand of Fear", one-shot villain Eldrad regenerates from a female incarnation into a male one, becoming the first on-screen cross-gender regeneration. Eldrad is a Kastrian rather than a Time Lord, but specifically tells the Doctor that, as a Time Lord, he should already know such things are possible.
  • K9's voice actor changed in Season 17 from John Leeson, the person most associated with the role (he's still voicing the character to this day), to David Brierley. 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 K9.
  • Yet another Time Lord (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 (Alex Kingston), 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 "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 Race Lift 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 Ace but never carried out due to the cancellation of the show.
  • Not only is changing race possible, so is changing gender. Though first seen in a parody special, the Doctor later mentions a friend named the Corsair in "The Doctor's Wife", who had the same tattoo in all his — or her — regenerations. This was further confirmed as canonical when Missy appeared as the first female incarnation of the Master.
  • "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.
  • Real Life Writes the Plot in the case of the Rani; Kate O'Mara played the original Rani but passed away suddenly in 2014, causing Actor Existence Failure before returning for a Big Finish audio; her wishes were for someone else to take on the role and the Rani regenerated, with Siobhan Redmond as the new incarnation.
  • This wasn't the first time Big Finish had created a new incarnation of a Time Lord due to the death of the original actor — a number of audios feature Graeme Garden and Rufus Hound as later incarnations of the Monk, replacing the long-dead Peter Butterworth. Then Gemma Whelan was cast as the first female incarnation, the Nun.
  • Spoofed in the Doctor Who 50th anniversary Google Doodle, a simple game about negotiating territory and running away from Daleks. Every time the player died, they regenerated into the next Doctor.
    • LEGO Dimensions 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.
    • Matt Smith, playing the Eleventh Doctor in a short video clip for the 50th Anniversary celebrations, claimed that he'd just returned from the 100th Anniversary celebrations, at which all fifty-seven Doctors had been in attendance.
  • Catherine Tate, who arguably played a Doctor of sorts in "Journey's End" — the "Doctor-Donna", an alter ego created from being exposed to his regeneration energy, which at first had no side effects until she was struck by a jolt of electricity. This awakened the Doctor's personality and intellect inside her head, on top of her human psyche. However, Donna's mind began to overload from having two personalities working at the same time, and the Doctor was forced to block her memories of him forever so that she would lose the awareness of her "Doctor-Donna" self and the "Doctor" half of her mind would be switched off.
    • Given River's more successful in utero Bio-Augmentation (with a little help from the TARDIS), one interpretation is that, had Donna been young enough or met other energy-state criteria, she could have adapted and gone whole-hog. But Ten had a well-established habit of dithering with the whole process, from clones, to Donna, to his own regeneration, so could well have utterly borked it. It would certainly explain the crushing guilt the Doctor still carries over wiping her.
  • 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 Doctor Who New Adventures featured a new version of the Master physically based on Basil Rathbone, the Eighth Doctor Adventures introduced an antagonistic third incarnation of Romana physically based on Louise Brooks, the Past Doctor Adventures had a brief appearance from a dark-skinned future incarnation of Romana in Tomb of Valdemar, the Doctor Who Novelisations 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 androgynous child in a hi-tech wheelchair with a robot dog, in the novelisation of Rose, the Doctor Who Magazine 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 Doctor Who (Titan) 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 DWM strips also featured a future incarnation of the Doctor physically based on Nicholas Briggs in Seventh Doctor comic "Party Animals" (with another character impersonating him in Eighth's era), making his Doctor from Doctor Who Audio Visuals DWM canon.
  • The three incarnations of Iris Wildthyme who appear in the Eighth Doctor Adventures were physically based on Beryl Reid, Shirley Bassey, and the young Jane Fonda. When she subsequently appeared in Big Finish, she was voiced by Katy Manning.
  • In Engines of War, the Doctor, of course, gets a reference here and there about past lives, but Karlax regenerates from a somewhat wiry white man into a more tall, dark and muscular incarnation.
  • One recurring Big Finish character is a Time Lord criminal who has all of their previous incarnations still active in their mind, and is identified by the number of incarnations currently present (i.e. the One, the Two, the Three, and so on). Four of their incarnations have appeared in person: the Eight (Tim McMullan), the Nine (John Heffernan), the Eleven (Mark Bonnar), and the Twelve (Julia McKenzie).