When, why and how has Doctor Who's Master regenerated throughout the course of the series? Originally envisioned as the Moriarty to the Doctor's Sherlock Holmes, the Master has been the Doctor's arch nemesis since the show first made the transition from black and white to color, and has remained an integral part of Doctor Who's rich science fiction tapestry ever since. Presented as the intellectual equal to the Doctor, the Master is another renegade Time Lord, but one that has chosen to use their scientific brilliance to dominate and conquer, rather than to help others.
While a variety of Gallifreyans have appeared on Doctor Who over the years, the Master is the only one, other than the Doctor of course, that viewers have watched evolve over a long period, transitioning through a number of regenerations and taking on several sinister personalities. Despite their inherent differences, the Doctor and the Master have always enjoyed a love/hate relationship, and the two troublesome Time Lords have often teamed up against greater threats before breaking up again in dramatic fashion.
While the Master has regenerated many times, the process is generally different to the Doctor's, usually occurring unnaturally or off-screen. Nevertheless, the Master's fictional regeneration history is just as fascinating as that of the Doctor and full of dark twists and turns. Here are all of the Master's regenerations explained, only taking into account the absolute canon of televised material.
Roger Delgado
The original, and many would argue the best, Master was introduced in the Third Doctor story, "Terror of the Autons," as the mastermind behind an alien invasion of Earth by the Nestene Consciousness. Despite being the first Master to appear on screen, this iteration of the character is actually the Master's final natural regeneration, having previously renewed himself 12 times off-screen. Delgado helped shape the Master's appearance, persona and speech, and would go on to appear in a total of 8 stories across the Third Doctor's era. Tragically, however, Delgado passed away only a few months after the airing of what would be his final Doctor Who appearance, "Frontier In Space."
For obvious reasons, no regeneration sequence had been filmed and the closing moments of Delgado's final episode see him escape to torment the Doctor another day. The Master returns in "The Deadly Assassin," where it is revealed that the villain was found dying and decayed by Gallifrey's Chancellor Goth, who took him back to their home planet to embark on a dastardly plot together.
Peter Pratt & Geoffrey Beevers
The decaying, corpse-like Master seen in "The Deadly Assassin" was played by Peter Pratt, and there is some debate among fans as to whether this is a severely disfigured version of Delgado's Master, or whether this is the villain's final regeneration and Delgado was the twelfth. In either case, the Master is now dying and out of regenerations, and, in truth, his new grotesque appearance was nothing more than Doctor Who's workaround to reintroduce the character following the death of Roger Delgado.
The Crispy Master returned once again in "The Keeper Of Traken," still in a state of decay, but this time played by Geoffrey Beevers. Nearing a permanent death, the Master steals the power of the titular Keeper in an attempt to extend his life. While the Fourth Doctor manages to save the day, the Master uses his lingering Keeper powers to inhabit the body of Traken's Consul, Tremas, whose daughter would go on to become one of the Doctor's companions.
Anthony Ainley
After a period without human appearance, Anthony Ainley took Roger Delgado's place as the second actor to play the Master long-term. Though still technically on his final regeneration, possessing the body of Tremas gave the Master a new lease of life and Ainley continued in the role until Doctor Who was cancelled in 1989, coming up against a total of 4 separate incarnations of the Doctor.
Though this version of the Master brought back the cunning nemesis figure that had been absent since Delgado's death, viewers noticed how Ainley was evidently being instructed to closely imitate the original Master. Since Doctor Who was cancelled with Ainley still in the role, no regeneration sequence was filmed.
Eric Roberts
For the 1996 TV movie, Eric Roberts was cast as the new Master, but not before the villain reappeared as a mysterious snake-like creature. Following the end of the original Doctor Who TV run, it's revealed that the Master was captured and executed by the Daleks as part of a new peace treaty with the Time Lords. As per the Master's final request, the Doctor is charged with escorting his former foe's ashes and this trip gives the snake-like Master a chance to escape.
Wider Doctor Who media has revealed this creature to be a Deathworm Morphant; a creature the Master uses as a vessel to survive death. After breaking free of the Doctor's TARDIS, the creature slithers its way down the neck of Eric Roberts' paramedic character, Bruce. Just like Tremas before him, Bruce is killed by the Master's attack, and the evil Time Lord inhabits the human's body, giving himself physical form once again, but retaining the eyes of a serpent.
Derek Jacobi
Eric Roberts' version of the Master falls into the Eye of Harmony inside the Eighth Doctor's TARDIS and is subsequently imprisoned. While his misadventures here are well-documented in comics and novels, how the Master escaped is one of several inconsistencies between the movie and main TV series. The revived 2005 Doctor Who did confirm, however, that the Master was granted a new regeneration cycle by the Time Lords in their desperation to recruit powerful allies during the Time War.
In typical Master fashion, the character took his shiny new set of regenerations and ran away, using a Chameleon Arch to temporarily turn into a human and go undetected under the guise of Professor Yana, portrayed by Derek Jacobi. Coming into contact with the Tenth Doctor, the Master's memories are triggered, and he returns to his Time Lord state. Shocked by the sudden transformation of her once placid colleague, "Yana's" former assistant shoots and kills the Master, triggering his next regeneration.
John Simm
John Simm's Master experienced a rollercoaster of near-death experiences following his introduction as British Prime Minister, Harold Saxon. Using his hypnotic influence and an army of cyborgs called the Toclafane, the Master finally conquers Earth and defeats the Doctor, who he turns into Dobby the House Elf and keeps him as a pet on board his sky base. Thanks to the efforts of Martha Jones, the Doctor is able to return to his regular form and undo the Master's damage. Supposedly in revenge for her suffering, the Master's human wife shoots and kills her spouse and the Time Lord refuses to regenerate.
This is later revealed to be a ruse, as the Master's wife manages to revive her fallen husband in "The End of Time." After clashing with both the Tenth Doctor and Rassilon, John Simm's Master is taken to Gallifrey and "fixed" in return for helping the Time Lords take down their maniacal leader. Leaving Gallifrey, the Master takes over a Mondasian colony ship where he encounters Missy, his next incarnation, and the Twelfth Doctor.
Although the two Masters initially form an alliance, Missy ultimately chooses to fight the Cybermen alongside the Doctor and stabs her past self in the back, triggering her own regeneration.
Michelle Gomez
In retaliation for the aforementioned stabbing, John Simm's Master shoots Missy before beginning the regeneration process. Rather than simply heralding the appearance of a new Master, however, Simm's villain proudly claims that the laser blast was so severe that Missy won't be physically able to regenerate, and the Master will supposedly die for good.
Missy's fate has yet to be explored in Doctor Who. It's virtually guaranteed that the Master will return, possibly even in the forthcoming season 12, and there'll no doubt be an elaborate explanation as to how Missy survived her predecessor's attack. Whether fans will see Jodie Whittaker's Doctor face off against Missy or an entirely new Master regeneration, however, remains to be seen.
Doctor Who season 12 premieres in 2020 on the BBC and BBC America.