Matt Smith is the youngest actor to take on the role of the Doctor
By Tim Masters
Entertainment correspondent, BBC News
Matt Smith appears in the room, like a Tardis materialising out of thin air.
It's a rainy March afternoon at Doctor Who HQ, near Cardiff, and a small group of journalists is being given a guided tour of the costume department.
Suddenly, the new Doctor is striding among us - in full costume - with raindrops in his impossibly floppy hair.
"And this is the raggedy Doctor..." says Smith, pointing to a dummy wearing the scorched shirt and tie of David Tennant's 10th Time Lord.
Matt Smith's new Doctor makes his debut on Easter Saturday
It's what Smith wears during much of his debut episode The Eleventh Hour - which airs on BBC One on Easter Saturday.
After a quick chat about his tweed jacket and his bow-tie, the 27-year-old actor pops open his shirt buttons and reveals a circle of bare chest.
"I wear a grey T-shirt underneath with a hole for my mic," he says.
And then he's hopping on one foot, pulling up his trouser leg to reveal his microphone transmitter.
He may not be in character, but it already feels like we're getting to know Matt Smith's zany 11th Doctor.
"I was always very keen that the element of the professor would come out," says Smith, readjusting his clothing.
Karen Gillan plays the role of new companion Amy Pond
He describes how he prepared for the role in the first half of 2009, before filming began.
"I wrote loads of stories about the Doctor and Einstein in Egypt - that's how the pyramids were created," Smith explains excitedly.
"I had six months, and it was the only way that I could get in contact with the Doctor. I always picture Einstein like this..."
Smith sticks out his tongue in a recreation of the famous photograph of Einstein from the early 1950s.
And then - tongue retracted - he talks about how he wants his costume to evolve over the next two years.
"I want a coat - practically - because I get cold. And I'd quite like a hat..."
From a nearby mannequin, he grabs the policewoman's hat worn by his companion, Amy Pond, and puts it on his head.
"But maybe not in every episode."
'Process of evolution'
Matt Smith and Karen Gillan met the press and fans at the Cardiff launch
A few hours later, I'm sitting with Matt Smith in an almost-empty auditorium in a Cardiff multiplex.
It's a few minutes after the premiere screening of The Eleventh Hour - and he's trying to eat a Scotch egg in between interviews.
Is he ready for the wave of fandom that's about to hit him?
"I can only answer hypothetically because I don't know what it is yet," says Smith earnestly. "I guess you try and deal with it with as much grace and aplomb as you can.
"I'll go about my business and walk and get my paper at the same paper shop and all the rest of it. You've got to live your life."
He seems genuinely grateful when told he seems to have fitted easily into the role vacated by David Tennant.
"With my Doctor there's a process of evolution, and I hope that's part of the appeal of the series.
"I think I get better, as time continues and you get more confident and assured hopefully that transmits to the screen. But that's very kind of you to say - thank you - it means a lot."
Doctor Who's new show-runner Steven Moffat has described Smith as bringing "genuine madness" back to the role.
"I think every person that plays it brings something new," says Smith. "Tom Baker was pretty bonkers, so it isn't as though there haven't been bonkers Doctors before.
"I think my Doctor is quite reckless - he takes everything to the precipice and then jumps off and then BOOM! He'll have a moment of inspired genius."
The actor has revealed that he unwinds between scenes by playing the guitar.
"I'm not particularly good, I know about five chords and just riff around. But it does help me relax," says Smith.
"Music is one of my passions. I have a piano at home and I tinker on that. I like the sense of improvement you get with an instrument - it's different to acting, and it's a different bit of me to express and explore."
And then he's off to his next interview, gripping that Scotch egg as if it were as precious as the Doctor's sonic screwdriver...
Doctor Who: The Eleventh Hour can been seen on Saturday 3 April on BBC One at 1820 BST.