The transition to each succeeding actor is explained within the show's narrative through the plot device of regeneration, a biological function of Time Lords that allows a change of cellular structure and appearance with recovery following a mortal injury.

The episode "The Timeless Children" revised the Doctor's origins, revealing a scientist and space explorer named Tecteun who found a lone, mysterious child with a supernatural physiology – one not belonging to any other life form or species – and an immense intelligence.

[4] In "The Sound of Drums", the Doctor describes an academy initiation where, at the age of eight, Gallifreyan children were taken from their families and made to look into the Untempered Schism, a gap in the fabric of reality, to view the Time Vortex.

He was contacted by a Wraith who told him about the prophecy of a legendary creature known as 'the Hybrid', prophesied to have been crossbred from two warrior races that would stand in the ruins of Gallifrey, unravel the Web of Time and burn a billion hearts to heal its own.

According to this, he was a member of an organisation called the Deca, ten brilliant Academy students campaigning for increased Time Lord intervention, alongside Mortimus (the Meddling Monk), Ushas (the Rani), Koschei (the Master), Magnus (the War Chief), Drax, a spy named Vansell, Millennia, Rallon and Jelpax.

[8] In the Virgin Missing Adventures novel Goth Opera, it is said the Doctor was a frequent prankster while at the academy, introducing cats into Gallifrey's ecosystem with his friend Ruath and electrifying a "perigosto stick" belonging to his teacher, Borusa.

Once their first-born son announced the arrival of a baby, the family was targeted by the Lord President, as the child was to be conceived naturally and only the Loom-born could inherit the Legacy of Rassilon; as a result, the Doctor's children were systemically culled.

Newman was not keen on this idea and – along with several other changes to Webber's initial format – created an alternative lead character named Dr Who, a crotchety older man piloting a stolen time machine, on the run from his own far-future world.

In the first serial, An Unearthly Child, two teachers from Coal Hill School in London, Barbara Wright and Ian Chesterton, become intrigued by one of their pupils, Susan Foreman, who exhibits high intelligence and unusually advanced knowledge.

The Doctor's hypersensitive body and senses enable them to detect anomalies humans cannot, such as identifying alien species, blood type or chemical composition by taste and determining location or time period by sniffing the air.

Thanks to exposure to many of history's greatest experts, including those from the future, the Doctor is a talented boxer, musician, organist, scientist and singer (able to shatter windows with his voice), and has a PhD in cheesemaking ("The God Complex").

According to the in-vision commentary on the DVD release, David Tennant had to inform actress Sophia Myles (who played Madame de Pompadour) that she was not, in fact, revealing the Doctor's surname as she believed was the intent of the dialogue.

Since contradicted by the television series, the 2003 Telos novella Frayed by Tara Samms, set prior to the programme's first episode in 1963, presents the alternative explanation that the Doctor was given that name by medical staff on a foreign planet and liked it.

[citation needed] Several personality traits remain constant throughout the Doctor's incarnations,[20] most notably a disarming or mercurial surface, concealing a deep well of age, wisdom, melancholy, and darkness.

This duality is explored more overtly in the revived series (2005–present), which has described him as "fire and ice and rage, he's like the night and the storm in the heart of the sun, he's ancient and forever, he burns at the centre of time..."[48] and "the man who can turn an army around at the mention of his name".

[non-primary source needed] Often the Doctor is critical of others who employ deadly force, be they their companions (Leela in The Face of Evil and The Talons of Weng-Chiang (1977); Jack Harkness in "Utopia" (2007)) or other supporting characters.

Through the course of his adventures, the Eleventh Doctor underwent significant personality shifts, becoming ever more ruthless when travelling alone; falling into a deep depression and inertia when his friends Amy and Rory were lost to him, and finally undergoing a manic change at the prospect that Clara "Oswin" Oswald was still alive.

The Fourth Doctor's long frock coat, loose-fitting trousers, occasionally worn a wide-brimmed hat and trailing, multi-striped scarf added to his somewhat shambolic and bohemian image; the Fifth's Edwardian cricketer's outfit suited his youthful, aristocratic air as well as his love of the sport[citation needed] (with a stick of celery on the lapel for an eccentric touch, though in The Caves of Androzani (1984), it is revealed to turn purple when exposed to gases the Doctor is allergic to); and the Sixth's multicoloured jacket, with its cat-shaped lapel pins, reflected the excesses of 1980s fashion.

[citation needed] The Seventh Doctor's outfit – a Panama hat, a coat with a scarf, a tie, checked trousers and brogues/wing-tips – was more subdued and suggestive of a showman, reflecting his whimsical approach to life.

[54] The idea was grounded in branding considerations,[citation needed] as was the movement starting in Tom Baker's final season toward an unchanging costume for each Doctor, rather than the variants on a theme employed over the first seventeen years of the programme.

[58] The Twelfth Doctor wears a white shirt with no tie, with his top button fastened and no cuff links, a dark blue cardigan (sometimes replaced with a waistcoat), navy trousers and black boots.

Davies's 2018 novelisation of his debut episode "Rose" states that the Doctor's future incarnations include "a tall, bald black woman wielding a flaming sword" and "a young girl or boy in a hi-tech wheelchair with what looked like a robot dog at their side".

While his regeneration first appeared to be smooth ("The Parting of the Ways"), the Tenth Doctor began to experience spasms and became somewhat manic, frightening his companion as he pushed the TARDIS to dangerous extremes (Children in Need mini-episode).

Rose Tyler is seen holding an infant version of herself in "Father's Day", with no visible energy discharge, but the contact does allow the Reapers to enter the church in which the Doctor and several others are taking refuge.

The Master proceeds to age the Doctor further with his laser screwdriver, reducing him to a tiny, wrinkled being, subsequently imprisoned inside a bird cage until reverted to his current form with the help of Martha Jones, 15 satellites and the entire population of Earth.

Two people who are really crazy about each other..."[86] The narrative of series nine culminated in a three-part story arc in which Clara dies and the Doctor spends the next 4.5 billion years executing a gambit to change history and save her life.

In various novels – especially Lungbarrow – it is established that Time Lords do not reproduce sexually, but emerge from genetic Looms fully grown, though the same book hints that the Doctor's birth was an exception (unlike his cousins, he has a belly button).

In the Big Finish Productions audio play Loups-Garoux, the Fifth Doctor reluctantly agrees to marry the werewolf Ileana De Santos and although he gets out of it later, as in Cameca's case, a degree of mutual attraction is present.

In the audio plays involving the Eighth Doctor, his companion Charley confesses her romantic feelings for him in Zagreus, but although he admits he loves her at the time, it is a highly dramatic moment and the relationship does not progress beyond the platonic.

The recurring novel and audio character Iris Wildthyme, created by Paul Magrs, is first introduced in the Short Trips story Old Flames, is a past romantic interest of the Doctor's who continues to flirt with him whenever they meet.