Capaldi's portrayal of the Doctor starts out as a spiky, brusque, contemplative, and pragmatic character who conceals his emotions in the course of making tough and sometimes ruthless decisions.

Ben Daniels, who was an early favourite following the announcement of Matt Smith's departure,[2] said that he had been approached with a view to assessing whether he would be interested in playing the Doctor, with his name remaining as a potential contender until just before the live BBC broadcast.

[7] Ben Stephenson, the BBC's drama commissioner, said that Capaldi was suggested months before the August revelation and that a secret audition was held at Moffat's home.

He discovered he had been given the part during filming for Adrian Hodges' The Musketeers in Prague; after missing a call from his agent, Capaldi rang back to be greeted with "Hello, Doctor!

[27] Regarding his decision to leave, Capaldi stated that despite his tremendous love for the show, he was unsure if he would be able to deliver at his best performance if he remained in the role for too long.

[32] Writing for Radio Times, fashion columnist Anna Fielding described it as "a classic early skinhead look" and linked it to Capaldi's history as a punk musician.

In "The Magician's Apprentice", he wears Ray-Ban sunglasses (later revealed in "The Witch's Familiar" to be a wearable version of his sonic screwdriver), a T-shirt and plaid baggy trousers along with the hoodie and Crombie coat.

[48] Initially it was reported that Capaldi specifically requested that the Doctor will not flirt with his companion the way his previous incarnation did,[30] but the actor stated that he said no such thing and that it was inflated by the media.

"[56] Capaldi stated that part of the Doctor's personality would share "a certain acid wit" of Malcolm Tucker, "specifically the attitude, the wisecracks and the energy...he can be edgy, volatile and dangerous".

[65] For Series 10, Capaldi described his character as more "closed off" and "suspicious" than the previous season, he elaborated "If you've been following this Doctor, you've seen him go through all those different colours and all those different places, and as for where he goes now, I don't know, but he's been put through the mill."

In the series 8 premiere "Deep Breath" (2014), the Doctor arrives in Victorian London, where he recovers from the stress of his regeneration, initially under the care of the Paternoster Gang.

In the finale, he meets Missy (Michelle Gomez), the latest incarnation of his nemesis, the Master, who reveals that she conspired to bring him and Clara together and has begun converting the Earth's dead into Cybermen; her plan is to compromise the Doctor's morality with the offer of an army with which to rule the universe.

After a traumatic ordeal, the Doctor and Clara part ways, seemingly for good, before they are reunited by a shared dream in "Last Christmas" and agree to continue adventuring.

In "The Girl Who Died," the Doctor finally remembers that he shares a face with a man he was persuaded to save in Pompeii, despite his initial reluctance to alter the timeline.

He is inspired to resurrect Viking girl Ashildr (Maisie Williams) with alien technology; he learns in "The Woman Who Lived" that she has become immortal and watches over his past companions.

In "Face the Raven", Clara dies while trying to outsmart Ashildr, who stages an elaborate ploy to trap the Doctor, which he learns in "Heaven Sent" was on behalf of the Time Lords.

[71] In the series 10 premiere "The Pilot" (2017), it was revealed that the Doctor has spent decades working as a professor in St Luke's University in Bristol, giving lectures on time and life, assisted by Nardole.

Over "The Lie of the Land", "Empress of Mars" and "The Eaters of Light", the Doctor becomes more convinced that Missy has reformed her ways, and so in "World Enough and Time", he sends her to react to a distress call on a colony ship trapped in the gravity of a black hole.

His plan goes horribly wrong when Bill is shot and converted into a Cyberman by medics in the lower floors of the ship, where due to time dilation many years go by.

New Series Adventures released novels starring the Twelfth Doctor and Clara Oswald in September 2014: Silhouette, The Crawling Terror, and The Blood Cell.

Following the broadcast of "Deep Breath", Euan Ferguson of The Guardian called his performance "wise and thoughtful",[80] while Michael Hogan of The Telegraph felt that Capaldi's portrayal "crackled with fierce intelligence and nervous energy".

Club, stating "Capaldi turns in a suitably fearless performance, reaching his obsessive crescendo as he prepares to meet whatever is waiting for him at the end of the universe".

[82] His acting in "The Caretaker" was praised by Morgan Jeffery of Digital Spy, noting "Capaldi's is the most complex and variable take on the Time Lord we've seen since Eccleston".

[89] Steven Moffat praised his leading man, stating "we could argue for the rest of our lives about who's the best Doctor — but for me, the best single performance in the role is settled forever.

[92] In a later interview, Baker expressed that Capaldi initially had "a rough deal" as fans weren't very kind towards his incarnation, as they had been conditioned towards "eye candy" in the form of "dashing role model[s]" popularised by David Tennant.

[93] Den of Geek' Simon Brew lauded Capaldi in "Before the Flood" noting "his performance continues to mix grumpiness, friendliness, intelligence and a large dose of alien".

[95] His performance in "The Zygon Inversion" was heavily praised by with Dan Martin of The Guardian, stating "this Doctor has never been written better, Capaldi has never channelled Tom Baker more".

[102] Mulkern of Radio Times praised Sarah Dollard's writing of the Doctor in "Thin Ice", noting how she "examines his moral code; the ideals he aspires to and the crimes and misdemeanors he's prepared to indulge".

"[105] Capaldi received overwhelming praise for his performance in "The Doctor Falls", with Radio Times's Mulkern noting the episode as a story dedicated to the character and how he "stands tall".

[107] Brew of Den of Geek heavily praised the actor's performance, writing "If you needed a reminder of just how much he's going to be missed when he finally departs Doctor Who at the end of the year, his outstanding work here was precisely that".