Peter Capaldi is an older, wiser ‘Doctor’

Taking on the lead role in “Doctor Who” is a life-changing gig for any actor. After five decades, the Doctor has become one of the most iconic characters in British television — and, increasingly, all over the world.

But few come to the part with as much unabashed fandom as Peter Capaldi, the 56-year-old actor making his debut in Saturday’s season premiere.

“As a kid, I thought if you looked hard enough, you might find the TARDIS [the Doctor’s time machine] somewhere,” Capaldi recalls in his Scottish brogue. “It could be in your backyard; it could be behind the library. The Doctors I grew up with were like the Wizard of Oz — they had a magic about them.”

Fans of Capaldi’s performance as an acid-tongued spin doctor on the British show “The Thick of It” are familiar with his invective. And though there’s no cursing on “Who” — its origins are as a children’s show, after all — the characters share a temperamental link.

Unlike his predecessor, the youthful and chipper Matt Smith, Capaldi’s gray-haired Doctor is prickly. He is — as the first episode puts it — nobody’s boyfriend.

“He’s brusque,” agrees showrunner Steven Moffat. “But the Doctor has always had the capacity to be phenomenally rude.”

“He’s impatient,” says Capaldi, “because he’s passionate and he can go anywhere in time and space. I wanted to make him someone who could see beauty in all kinds of things. But he’d only offer you a chance to come with him once. If you hesitate — he’s gone.”

Capaldi should know the canon by now; he’s been prepping for the part his entire life. As a teenager, he even drew “Doctor Who” art, published in a fan newsletter. He’s had a long and varied career, getting his start in the acclaimed 1983 film “Local Hero,” but this role is more than a job. “Everyone has such a joyful reaction to you,” he says of the fans he’s met thus far. “I think ‘Doctor Who’ is a good thing in the world.”

Capaldi, who lives in London with his wife of over 20 years and their teenage daughter, is clearly a young-at-heart Doctor despite the show’s plentiful age jokes.

“They threw me out of an airplane,” he says delightedly. “Everybody was worried, saying, ‘Don’t stay up there too long!’ I wanted to stay up there all day! It was like being a 9-year-old.”

What’s the most affecting part of being a fan-turned-star? “The first time you have an exchange with a Dalek,” he says, referring to the show’s longstanding villain. “You think you know Daleks. But there’s a bunch of them. There’s Renaldo; he’s an Italian Dalek, he only speaks Italian. There’s Barnaby, the lead Dalek — very articulate. But when they get together and it all works and they’re talking to you … wow, man! It’s really powerful. Of course, then one of them will bump into a wall or fall over or something.”

There’s a brand new character on the show this season: Capaldi’s expressive brow, made much of in the first episode. “I’ve never been terribly conscious of my eyebrows,” he says. “And now it’s got to the point where, if the script would say, ‘The Doctor looks concerned,’ now it just says, ‘Eyebrows.’”