The Scottish actor was named the new star of the British sci-fi franchise Doctor Who on Sunday during a live broadcast on BBC America. He will replace the departing Matt Smith, whose time in the time-traveling police box the TARDIS ends later this year.
"It's so wonderful not to keep this secret any longer," said Capaldi, a lifelong fan of the show. "I haven't played Doctor Who since I was 9 on the playground."
Capaldi, 55, becomes the 12th man to play the Doctor since the cult show debuted in 1963 with star William Hartnell and the fourth Time Lord since executive producer Russell T Davies rebootedDoctor Who in 2005, following Christopher Eccleston, David Tennant and Smith.
Executive producer Steven Moffat had considered Capaldi when they were casting the 11th Doctor. "There comes a right time for the right person to play it," he said.
"We all had the same idea and it was a quite different idea," Moffat added. When he and his team made a video with Capaldi, "everybody saw it and was like, 'That's the Doctor.' "
American audiences most recently saw Capaldi as a World Health Organization doctor in the movie World War Z, and he also has big-screen roles in the upcomingThe Fifth Estate this fall and next year's Maleficent.
The half-hour live special on BBC America, hosted by British TV personality Zoe Ball, also featured past Who stars, including Peter Davison, the fifth Doctor (1981-84).
"In a way it's the longest job in television. It's a whirlwind time when you do it, and it keeps on going after," said Davison, whose daughter is married to the 10th Doctor, Tennant.
Smith recalled that people initially met his casting with backlash, but fans ultimately came around for him as the Doctor.
"There are no parts like this," he said. "I loved it, I'll miss it, but when you gotta go, you gotta go."
Doctor Who has long been a hit in the U.K., but more recently the Doctor has gained a huge following in the USA, with the show becoming the highest-rated series on BBC America.
Capaldi will make his first appearance in the Doctor Who Christmas Special at the end of 2013, and it marks Smith's final jaunt as the Doctor. Fans get to see him one more time, though, when Smith stars with Jenna Coleman, John Hurt and Tennant in the 50th anniversary special airing on Nov. 23.
The main reason the series is still a fixture in global pop culture is because of anybody who's ever watched it, Capaldi said. "Doctor Who belongs to all of us. Everybody makes Doctor Who."