At the age of 55, Peter Capaldi is the second-oldest Doctor ever (he'll be just two months younger than William "grandfather" Hartnell was at his first appearance in the role) and follows the youngest ever, Matt Smith, and two relatively youthful predecessors.
But while some are wondering how an older Time Lord will go down with the show's younger fans, showrunner Steven Moffat says Matt Smith helped ensure the time was right for Capaldi's new twelfth Doctor.
"I think it's good we've got a different age [of Doctor]," said Moffat. "Because I cannot imagine what somebody in their twenties would do with the Doctor after Matt showed us all how to be a twenties Doctor.
"I don't know what you would do after that because he was so perfect."
Moffat revealed that Capaldi's name had briefly occurred to him when he was casting the eleventh Doctor. He had quickly dismissed the thought but said Matt Smith's four years in the role had prepared it for Capaldi.
“[Peter Capaldi] did flick through my mind when we were replacing David [Tennant]," said Moffat, "and he didn't feel right at all. And I think when you think about that it wouldn't have been right. Not then. But there's something about Matt’s Doctor that paves the way for Peter’s Doctor.
"That's the important thing to remember about the Doctor – it's one character going through his life played by a succession of different actors and you have to get to that place each time.
"I can absolutely believe that the strange old-young Matt Smith will turn into the strange young-old Peter Capaldi.”
Capaldi was unveiled as the new Doctor during a live BBC1 show on Sunday night. Matt Smith will regenerate into Capaldi's twelfth incarnation in the seasonal special on Christmas Day.
Capaldi is best known as foul-mouthed spin-doctor Malcolm Tucker in BBC political satire The Thick of It.
Vote for Radio Times's iconic Dalek cover in the magazine Cover of the Century award