(CNN) -- BBC science-fiction series "Doctor Who" originally premiered in 1963, enticing viewers with its depiction of a time traveler known as the Doctor who explores the universe in a spaceship called the TARDIS. The series has since aired 33 seasons and nearly 800 episodes with 11 actors portraying the Doctor over time.
Matt Smith, the 11th Doctor, set off a bit of frenzied speculation last month when he announced he'll be leaving the show. The BBC has said it will debut a new doctor in a Christmas special. As fans eagerly await the new appointment of the good Doctor, the network will celebrate "Doctor Who's" 50th anniversary with a biopic film about the show's origins.
"An Adventure in Space and Time" will premiere later this year (the air date hasn't been announced) and fictionally recounts the creation of series while exploring the team behind its first episode. "Sherlock" TV series creator and actor Mark Gatiss wrote the script, and "Game of Thrones" actor David Bradley stars as William Hartnell, the actor who played the first Doctor.
Gatiss and Bradley appeared at the recent Comic-Con in San Diego to promote the upcoming film and spoke with CNN on the red carpet for a party for "The World's End," which also stars Bradley.
The motivation behind the "Doctor Who" film, directed by Terry McDonough, is to celebrate the 50th anniversary of the popular series and to depict what Gatiss says is an interesting story.
Gatiss says that he's a lifelong "Doctor Who" fan and that he first tried to make the film on the 40th anniversary but ran into some difficulty as the series had not yet returned to the air. Fans know and love the story of how the show was created, he said, and he wanted to share it with them.
"It's a remarkable bunch of people, all of them misfits really," Gatiss said. "They cast as the Doctor William Hartnell, who had been typecast before that, and he got this role that totally changed his life. There's all sort of wonderful incidental details that made the show what it is today. It's a very moving story but broadly very celebrational. It's lovely to turn back and see how something you love took its first steps."
Hartnell had appeared in various plays and films before being cast as the first Doctor, the role for which he is largely remembered. The film explores the life of the original "Doctor Who" star as much as it does the series.
In portraying Hartnell, Bradley said he immersed himself in the early episodes.
"I wanted to see as much as I could to play him," Bradley said. "And of course in the film, we recreated a lot of the very first episode. Not only the first episode but the first pilot that was rejected."
Bradley said he was fascinated by watching Hartnell develop the character.
"He realized he was playing it too grumpy and authoritarian and lacking in humor," Bradley said. "I think as it went on he grew to love the part and felt ownership for it."
"An Adventure in Space and Time" is meant to be enjoyed by those who don't regularly follow the lengthy TV series or understand its extensive mythology, he said.
"It stands alone," Bradley said. "It's a very complex piece about lots of very interesting people."
Gatiss added, "That was my intention from the beginning. A lot of the films I admire the most, in terms of biographical films, succeed because you get involved with the person's story, not because you know all the things."
Part of "Doctor Who's" premise is that the Doctor can regenerate his body when he nears death. The concept explains the rotating actors who have portrayed him throughout the years.
During a Comic-Con panel about the film and the show's 50th anniversary, the creators confirmed the casting of the next doctor has not been solidified. "An Adventure in Space and Time," which is likely to premiere this fall on the BBC, will give fans an opportunity to see new content before the new Doctor is revealed in the Christmas special.
"Doctor Who" has been a seminal TV series, particularly in the UK, and Gatiss says he feels it may be because the character and premise are fundamentally unique.
"It's a great idea, and there aren't many of those around," Gatiss says. "But I think one thing is very important to say -- the Doctor is a television original. He's not based on a literary character. It's a character created by people in television for television, and it's still going strong 50 years later. That's very, very special."