There's no denying that every franchise's goal is to maintain its longevity and that is through constant reinvention. Safe to say the Doctor Who series has done just that, holding the record of the longest-running sci-fi fantasy show that never seems to lose its shine in its continuity.
That said, here's how and why the Time Lord regenerates.
Can the Time Lord Actually Die? Is He Immortal?
One of the most basic reasons the Doctor Who series keeps on coming back for more seasons is the inclusion of constantly changing its actors to play the titular Time Lord.
Now, as the title suggests, his lifespan likely has something to do with immortality, no?
Considering that he's been entrusted with the blue box (smaller on the outside, bigger on the inside) TARDIS (Time and Relative Dimension in Space) means he basically protects the universe on his travels.
Now, you'd have to be a pretty important species to have been provided with one of the greatest powers to claim in the galaxy.
There had been some indications that the Doctors were of alien species, especially since he admittedly has two hearts, which already indicates how much he can cheat death based on that alone.
However, the regeneration process he has to go through is what essentially keeps him alive.
It repairs and renews his cells whenever he's 'about to die.' However, the death here is called 'regeneration', in preparation for having the replaceable titular role for more actors to take which would keep the series going.
Now, the Doctor can die from many causes (i.e. old age as the First Doctor did, and the Ninth Doctor sacrificed himself to save Rose Tyler), but this merely triggers the time for him to regenerate into a different actor.
The Catch Behind the Doctor's Regenerative Powers
Initially, the showrunners declared that the Doctor can only ever regenerate 12 times, which means 12 actors, and not necessarily simply 12 seasons, as noted by a 1966 production note.
By the time Matt Smith's Doctor (the Eleventh Doctor) came into the picture, it was only a matter of time before the sci-fi series would reach its end.
However, when The Death of the Doctor episode came into view, it was right then and there, that a major character Clyde Langer (Daniel Anthony) asked how many times the Time Lord could regenerate.
At the time, BBC addressed this plot hole through the episode by saying that there is no limit.
Another time was during the Battle of Trenzalore, when the Eleventh Doctor was granted a new set of lives by the generation of Time Lords.
Although the implication of just how much more he can regenerate wasn't explicitly said, 'replenishing' a new set of lives could mean another set of 12 times.
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Here's Why the Doctor Regenerates
When the Doctor regenerates, you'd notice that the only thing he maintains is his character's origins, which is the fact that he is a Gallifreyan.
Although many seem to dismiss this theory, given it has never been confirmed, he is most comfortably called a Time Lord. In spite of his human-like appearance and human-like mannerisms, the Doctor is not human at all.
Part of the quirk of meeting every actor's version of the Doctor is how they bring a different type of character after every regeneration.
The Doctor often changes his clothes and makes comments about his own appearance (a random choice at that), and his personality, as well.
The Thirteenth Doctor (Jodie Whittaker) marked a whole new generation to the series, considering she was the first female Doctor after coming from a long line of male Doctors.
The next to set the milestone comes from Sex Education's star Ncuti Gatwa's Fifteenth Doctor.
It goes without saying that David Tennant (Tenth Doctor) is undoubtedly the most prominently known and popularly beloved Time Lord, considering he's the only actor who ran for three seasons since 2005.
He's the most fan-favorite to have played the titular traveler, and this is apart from his frequent appearances such as The Day of the Doctor, and now, he's returning as the Fourteenth Doctor in the Doctor Who 60th Anniversary.
While it remains to be seen as to why he regenerated into a past Doctor, all will be revealed once November comes.
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