Doctor Who? After months of febrile speculation the BBC tonight revealed the identity of the 11th Doctor. Not a prominent black actor, nor a woman, nor any of the high-profile names touted to play the iconic Time Lord.

Instead, the honour of wielding the sonic screwdriver and battling Daleks and Zygons has fallen to relative unknown Matt Smith – at 26 he is the youngest Doctor in the 45 years since the Tardis first landed at the BBC.

Smith, from Northampton, whose TV debut was in the 2006 adaptation of Philip Pullman's The Ruby in the Smoke, which also starred former Doctor Who companion Billie Piper, said he was so excited at landing the coveted role he paced his room for three days smiling to himself. "I'm flabbergasted. I haven't slept, really, to be honest," he said.

His unveiling as the next extraterrestrial scientist came during Doctor Who Confidential – The Eleventh Doctor, broadcast on BBC1 at the same time as being simultaneously cast on giant screens in city centres all over Britain.

Smith will replace David Tennant, 37, who will leave after filming four specials, and take over the role in October 2010.

Doctor Who executive producer Steven Moffat said he knew he had found his Doctor at the start of auditions. "The way he said the lines, the way he looked, his hair. Everything was spot on," he said, praising Smith's dynamism and swagger.

Whovians, too, were impressed. "We think it is a great choice to have someone so young. David Tennant was the most energetic Doctor ever, and you need somebody with youth and energy to take that forward," said Sebastian Brook, editor of the drwho-online fan website.

Punters had tipped Paterson Joseph, one of the stars of the recent Survivors sci-fi series, and Golden Globe winner Chiwetel Ejiofor as contenders for the first black Doctor, while Catherine Tate and Catherine Zeta Jones had been suggested as female doctors.

But Matthew Sweet, cultural commentator and broadcaster, said: "The idea of a black or woman Doctor is something we only seem to be able to enjoy as a tease. When Tom Baker left, for example, there was speculation about Joanna Lumley taking over. There is a little part of me that's disappointed the Obama effect hasn't reached Gallifrey yet."

Sweet, a lifelong Doctor Who fan, added: "This was one of the best kept secrets. Matt Smith has got a fascinating face. It's long and bony, with a commanding jaw. He looks like someone who could have been in Duran Duran. He has a quality of the old man trapped in the young man's body.

"I suspect he might be a more sensual character than David Tennant, who had no kind of dangerous sexuality about him. There's something Byronic about Matt Smith – he's got the lips for it."

Sophie Aldred, who played companion Ace opposite Sylvester McCoy's Doctor, said: "I'm delighted. I'm so pleased that they haven't chosen a big name but gone with someone who's obviously a good actor but not well known to the public at large.

"He's got a very interesting face and a fantastic presence. It's going to be a difficult job to follow David Tennant, but I think he'll be a safe pair of hands."

Smith, a former headboy, took up acting after hopes of a professional football career were dashed by a back injury. He appeared in Alan Bennett's play The History Boys at the National Theatre in London, and in Swimming with Sharks in the West End. Two of the productions in which he featured – That Face and On the Shore of the Wide World – won Laurence Olivier Awards.

In 2007, he had a leading role in BBC2's political drama Party Animals, in which he played a parliamentary researcher.

Seemingly unphased by landing the Holy Grail of TV roles, or the challenge of playing a 903-year-old, Smith said: "I'm just so excited about the journey that is in front of me."

Piers Wenger, head of drama at BBC Wales, said: "With two hearts, a ferocious mind and over 900 years of experience behind him, it's not every 26-year-old actor who can take on the role like the Doctor but within moments of meeting Matt he showed the skill and imagination needed to create a Doctor all of his own."

Tennant, who announced he was leaving last year, said: "As I begin the end of my connection to all of this, I do feel a bit of jealousy of Matt who's just about to start and has got all of this ahead of him, and it's a very exciting journey to go on."