Who's the Doctor?

He is a Golden Globe-winning black actor who has played a cross-dresser, a lead in a Richard Curtis rom-com, and a militant leader in a post-apocalyptic thriller. Now he is among a group of actors fighting to pull on the long coat of Britain's most celebrated time traveller.

This week, after an industry screening of the festive special, to be broadcast on Christmas day, the 34-year-old actor Chiwetel Ejiofor, known for performances in Kinky Boots, Love Actually and Children of Men, joined a slew of others vying become the next Doctor Who. The current Doctor, David Tennant, is set to depart from his role in the BBC1 sci-fi series late next year. According to William Hill, Ejiofor is currently second favourite behind Paterson Joseph. If either takes the part, it will be the first time a black actor has done so.

Tennant invited speculation about the next doctor when he announced he was to stand down after filming four episodes to be broadcast next year. "When Doctor Who returns in 2010 it won't be with me," he said. Tennant's departure may be speeded up, though. The actor had back surgery earlier this month and is struggling to film his final episodes.

Doctor Who's writers escape from the embarrassment of recasting their lead actor by writing his changing appearance into his back story. Time lords such as the Doctor have a biological ability to "regenerate" when old or wounded to assume a new physical form and personality. This Doctor's regeneration first happened in 1966, when William Hartnell, who was 58, was becoming difficult to work with. It was written into the script that Hartnell would collapse from exhaustion. His facial features then shifted into those of second doctor, Patrick Troughton.

Fast forward to an episode in July 2008, when the Doctor apparently started the process of regeneration, but did not complete it. David Morrissey emerged as a front-runner after it emerged that the Yuletide special, in which he stars, is called "The Next Doctor".

Chiwetel Ejiofor – 6/1

Chiwetel Ejiofor's casting would be a major coup. He has the experience, the profile, and is attractive to the ladies, helped by his Hollywood career. He had his first role in 1997 film Amistad, but his true breakout came five years later in the Stephen Frears-directed Dirty Pretty Things, in which he starred with Audrey Tautou as an illegal immigrant. Stephen Frears reportedly resisted pressure to consider better-known American actors in favour of the then little-known Ejiofor. The actor's profile has risen steadily; he was in 2003's Love Actually, followed in 2004 with a role in Spike Lee's She Hate Me. He has played in 2005's Kinky Boots, Children of Men (2006), American Gangster (2007) and, earlier this year, an award-winning turn as Othello with Ewan McGregor at the Donmar Warehouse.

Catherine Tate – 25/1 (Odds on the next doctor being female is 8/1)

The most flamboyant choice for the Doctor, female comic Catherine Tate has also been hotly tipped to take over. In 2006 she appeared as a special guest star of that year's Doctor Who Christmas special, The Runaway Bride, before returning to the show to play the Doctor's sidekick Donna Noble in a 13-week run from April this year. However, at the end of the series, her part was written out. Russell T Davies set gossip mills turning in a recent interview when he suggested a female Doctor Who might be a strong possibility. "I think kids will not have a problem with a female Doctor," he said. There has been speculation over female doctors before. Joanna Lumley was tipped to take over in 1981, but Colin Baker got the job.

David Morrissey – 3/1 (odds by William Hill)

Tennant's co-star David Morrissey in the BBC drama Blackpool has been given good odds to moving his belongings into the Tardis. Morrissey would be a safe pair of hands – and would bring a steely sensitivity to the part. He will star with David Tennant in next week's Christmas special of the series, and has versatility on his side. The actor has played everyone from a Nazi officer ( Captain Corelli's Mandolin) to a small-time casino boss ( Blackpool) to Gordon Brown ( The Deal) to Sharon Stone's love puppet ( Basic Instinct 2). "Everyone will be watching the programme and I don't really want to spoil what happens," Morrissey said in an interview earlier this month. "A lot of interest has been sparked by it. I am getting a lot of phone calls from people I have never met. I did love every minute of doing it. Whoever takes over has got big boots to fill."

James Nesbitt – 10/1

Cold Feet star James Nesbitt is in the running after Tennant was quoted as saying: "It's Jimmy Nesbitt who will be taking over. Jimmy Nesbitt got into touch to say 'please tell them it's not me. I spend all my day going round saying it's not me. I couldn't take over from David'." Nesbitt is a happy-go-lucky fellow and could bring a cheeky dose of humour, something Tennant has been adept at doing. However, speaking to Graham Norton on his television show in the summer, Nesbitt denied he was up for the part. "I know nothing about that. I wouldn't put a lot of money on it," the actor said.

Paterson Joseph – 4/6

Joseph has often been mentioned as the actor in the running to become the 11th Time Lord. Crucially, he has Doctor Who experience and is a science fiction fan, so would no doubt bring enthusiasm to the role. He has already appeared in two episodes of the show playing Roderick alongside previous doctor Christopher Eccleston. He starred in the BBC drama Jekyll, written by Steven Moffat, who takes over from Russell T Davies as the show's chief writer for its fifth season in 2010. In an interview with the BBC last month, Joseph, better known as creepy loans manager Johnson in Peep Show, said "any actor would love the challenge" of playing the Time Lord. But he refused to comment on reports that he is in the running for the part.