Thanks to the character's handy ability to regenerate into new bodies, Capaldi is the show's 12th lead actor. He's set to leave after a 12-episode series that begins airing Saturday on BBC television in Britain and BBC America in the U.S. (7 p.m. and 10 p.m. Saturday locally).
Reflecting on his time in the Tardis, the Scottish actor says he tried to make his version more elusive than those of Christopher Eccleston, David Tennant or Matt Smith, the three others who have held the role since "Doctor Who" returned in 2005 after a 16-year gap.
"I wanted him to be more difficult to know," Capaldi told the Associated Press during an interview in London. "I love what the show has done, and I love Matt and David and Chris. But they were all very accessible and very user-friendly. So I wanted the Doctor to be more distant from human beings.
"Avuncular is easy," Capaldi added. "I think it's more fun when he's abrasive and distant."
Capaldi's final series brings the Doctor a new traveling companion: Pearl's Mackie's intelligent, impetuous Bill Potts, first encountered slinging French fries in a university cafeteria. Trailers promise fan-favorite monsters including robotic Cybermen and the pepperpot-shaped Daleks, as well as the return of Doctor's arch-enemy, the Master.
Capaldi's successor is expected to be announced in the next few months and unveiled in a special episode at Christmas. It's a sign of the show's popularity that British bookmakers are offering odds on the next Doctor. Favorites include "Love, Actually" actor Kris Marshall and the actress-writer Phoebe Waller-Bridge. There's never been a female Doctor and many fans think it's about time.
Capaldi, 58, was something of a surprise when he was chosen in 2013. He was older than any Doctor since Hartnell, with a long film and television resume that ranges from the beloved 1983 film "Local Hero" to the zombie thriller "World War Z." And he had already created one iconic character, the foul-mouthed spin doctor Malcolm Tucker in the political sitcom "The Thick of It."
But Capaldi, a lifelong "Doctor Who" fan, says when he was approached about the role he "thought it was fate."
"I thought, you loved this so much as a kid you can't not do this," he said.
His affection has managed to survive what he calls the "television factory" of making one of the BBC's biggest exports.
"You've got to sort of be a grown-up actor to get through it, to get through the factory," he said. "(But) sometimes you need the little kid to come and whisper in your ear and say, 'There's a Dalek over there,' or 'You're standing in the Tardis.' And that kind of gives you a boost."
Capaldi is still recording his final episodes but intriguingly says "I have filmed dying." Faithful to the code of silence around the show, he will give no details about the Doctor's regeneration.
As for what gives "Doctor Who" its magic, Capaldi suggests it's the show's indefinable mixture of the silly and the profound.
"It has a kind of death motif in it," Capaldi said. "The Doctor dies, but doesn't. He survives as a memory. Even though there's a new one, he's still around. And I think that's a thing that people subconsciously kind of embrace.