Regeneration is one of Doctor Who's oldest and most important concepts, but how does the Doctor change their actor and look so regularly?
Doctor Who introduced regeneration in 1966 as the declining health of original star William Hartnell required a means to replace the Doctor actor. The concept has since been used over a dozen times to bring a new leading man (or lady) into the fray, allowing the British sci-fi sensation to continue its now-60-year legacy.
What Is Doctor Who's Regeneration?
When the Doctor (or any other Time Lord) is on the verge of death, they can regenerate all the cells in their body into an effectively new person. The painful process can give the Doctor a new appearance, race, personality, and even gender while holding onto the memories of their past.
Doctor Who had always maintained that a Time Lord could only regenerate 12 times, allowing for 13 incarnations before their unfortunate death. While the concept may initially appear simple, recent seasons delivered some twists that changed the game of regeneration—more on that later.
The Doctor's regenerations grew more complicated around the show's 50th anniversary as the series unveiled John Hurt's War Doctor. The debut of this Doctor proved to be a major revelation for viewers, as Doctor Who introduced a previously-unseen incarnation who existed between the 8th and 9th Doctors.
The secret War Doctor and a complicated second regeneration from the 10th Doctor (David Tennant) to keep the same face left the 11th Doctor (Matt Smith) technically being the 13th incarnation and on the verge of death from old age in "The Time of the Doctor."
That was until the Time Lords sent a gust of regeneration energy through a crack in time, granting him a new cycle of 13 lives enjoyed through Peter Capaldi, Jodie Whittaker, another David Tennant, and Ncuti Gatwa.
However, several years ago, during Jodie Whittaker's era leading Doctor Who, showrunner Chris Chibnall delivered a controversial retcon to the concept of regeneration - the Timeless Child.
Doctor Who's Major Regeneration Retcons Explained
During the Series 12 finale, "The Timeless Child," the villainous Master unveiled some shocking secrets of regeneration and the Doctor's once-hidden past.
A woman called Tecteun came from a species called the Shobogans, the indigenous people of Gallifrey. Once upon a time, Tecteun discovered an unknown being next to a monument beneath a wormhole to another universe.
The Shobogan adopted the child and uncovered their mysterious ability to regenerate after suffering a fatal cliff fall. Tecteun would study the power and even harness it herself to acquire the ability to regenerate.
She then shared this ability with other Shobogans to create the first Time Lords, restricting the maximum number of regenerations to 12.
A game-changing twist revealed the Timeless Child was, in fact, the Doctor, who ultimately had their memories wiped by Tecteun as they were forced to become a child who would grow up to become the first on-screen Doctor (William Hartnell).
Fans were introduced to one of these pre-Hartnell regenerations with the Fugitive Doctor (Jo Martin). This particular Doctor worked for the shadowy organization of the Division on Gallifrey until abandoning her responsibilities to become a fugitive, hiding away on Earth and taking on the human identity of Ruth Clayton.
And that all came before current showrunner Russell T. Davis threw another spanner in the works in the 60th-anniversary specials - bi-generation.
[ Doctor Who's Bi-Generation Twist Explained ]
David Tennant returned as a familiar face to play the 14th Doctor for the specials and was left on the verge of death in his battle with the Toymaker. As a result, the Doctor underwent a mythical bi-generation, splitting themself into two bodies - the 14th Doctor, played by Tennant, and the 15th, by Ncuti Gatwa.
The current era of Doctor Who is streaming on BBC iPlayer in the U.K. and Ireland and Disney+ in most other territories.
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