DOCTOR Who star and lifelong fan Peter Capaldi has compared being the Doctor to being the Wizard of Oz or Santa Claus.

Set to resume his role as the regenerating, time-travelling alien in the show's annual Christmas special, he said that the fictional character was treated as "mythical" by overseas fans.

Known for playing the less-than-family-friendly spin doctor Malcolm Tucker in The Thick Of It, Capaldi shot to international fame when he became the 12th actor to represent the Doctor, generating a particularly large fan base in South America.

He told the Radio Times: "I found it hard at first. You walk on stage and it makes people go crazy, not because you're me, because you're Doctor Who.

"When you see little kids, that's fantastic. A wee bit like being a mythical character, like the Wizard of Oz or Santa Claus."

At 58, Capaldi is one of the oldest actors to take on the role in its 53-year history, following the energetic performances given by Matt Smith and David Tennant.

But he told the magazine that the Doctor's age changes were crucial in making him accessible to all audiences.

"The Doctors I grew up with were not young," he said. "To me, Doctor Who was not a young man. Ironically, I'm older than any of those, except for William Hartnell.

"The thing about Doctor Who is the constitution of the audience.

"It covers a huge age range, so you have to entertain little kids and you have to entertain hipsters and students, and middle-aged men who should know better.

"So sometimes there is a kind of metaphysical and intellectual aspect to it, which is more to the fore than other times. But generally, we just blow up monsters."

The Doctor may see even further changes as lead writer and executive producer Steven Moffat is replaced by Broadchurch creator Chris Chibnall in 2018.

But whoever the creative brains behind the show are, fans have been coming up with their own theories about the Doctor's origins for years.

Having sent a fan letter to the show in 1974, when he was 15, Capaldi is one of them.

He said: "He's really not human at all. Who you see is what he has chosen to present, because that's the only way that humans can understand him and what he is."

"The truth is, he comprehends it too much. His problem is that he sort of knows everything. That makes life quite hard."

:: Read the full interview in this week's Radio Times.