Matt Smith leaving lead role in "Doctor Who"

Matt Smith is stepping down from the lead role in long-running sci-fi series "Doctor Who," spurring intense speculation about his replacement.

The BBC said Sunday that Smith will leave after a Christmas special November episode that will mark the show's 50th anniversary.

The titular Doctor is a time-traveling extra-terrestrial Time Lord who can regenerate into new bodies. Smith, who took over the role from David Tennant in 2010, is the 11th actor to play the character since the series began in 1963.

"'Doctor Who' has been the most brilliant experience for me as an actor and a bloke, and that largely is down to the cast, crew and fans of the show," Smith said in a statement. "I'm incredibly grateful to all the cast and crew who work tirelessly every day, to realize all the elements of the show and deliver 'Doctor Who' to the audience. Many of them have become good friends and I'm incredibly proud of what we have achieved over the last four years."

Stephan Moffat, lead writer and executive producer, added, "Great actors always know when it's time for the curtain call, so this Christmas prepare for your hearts to break, as we say goodbye to No. 11. Thank you Matt -- bow ties were never cooler."

"Doctor Who" is one of the BBC's most popular programs, and Smith's tenure has seen the show gain new fans in the United States, where it is shown on BBC America.

The BBC did not announce Smith's replacement, but fans took to the Internet to speculate about casting for the 12th Doctor.

Bookmaker William Hill made "Being Human" star Russell Tovey and "Harry Potter" alumnus Rupert Grint 10-1 favorites, followed by stage star Rory Kinnear and "Homeland" actor David Harewood.

William Hill also offered 8-1 odds on the next Doctor being female.