Actor Christopher Eccleston tells Newsround, in an exclusive interview, what it's like to play the lead role in Doctor Who.
He's the ninth actor to play the Doctor on TV. He's accompanied on his adventures in time and space by teenager Rose, played by Billie Piper.
Tell us about the Doctor.
He's 900 years old, he's got two hearts and he's a Time Lord from the planet Gallifrey. That's his basic CV.
He's a traveller in time.
He's had nine incarnations so far. He's brave, he's intelligent, he's funny, he's occasionally bad tempered, he's in love with life and he cares about life in all its forms - be it an alien from Venus or a kid who lives next door.
He's an enthusiast and he's insatiably curious and it's that curiosity that leads him into so much trouble and so many adventures.
What's the storyline
in episode one?
On planet Earth, there's this phenomenon where shop dummies - mannequins - are activating and attacking people. It transpires that they're being controlled by the Nestene Consciousness and they're about to take over the world.
What attracted you to the role of Dr Who?
The scripts - which are mainly written by a writer called Russell T Davies, whom I've worked with before.
The character was very different from anything I'd done before because he's very funny and light, and I've done a lot of heavy, serious drama.
Actors are only as good as the script they're speaking - and these are good scripts.
How did you get the role?
I emailed Russell T Davies and I asked him to put me on the list of people he was going to audition. And then I auditioned and they taped it, and I got the role.
What are your memories of Dr Who from childhood?
I wasn't a huge fan of the series but there are two things I did tune in for.
Firstly, the regenerations - when one actor took over the role of the Doctor from another actor.
I thought it was fascinating that it was the same character but he looked different, and I wanted to see how they did it special effects-wise.
And secondly, to see the inside of a Dalek.
The Daleks are the Doctor's greatest enemy and they are brutal and sinister and vicious but they also have something else going on inside them.
There were always a couple of episodes where that would be revealed. And that was fascinating - the psychology and the special effects. We have that in the new series.
Do you have a favourite Doctor?
No that would be wrong to say. The Doctors in my time were Patrick Troughton, who was the first one that I saw and in a way I lean towards him because he was the first one I saw.
I thought Jon Pertwee was fantastic and Tom Baker I also thought was fantastic.
Tell us about your relationship with Rose
They love each other. They're best friends and they kind of finish off each other's sentences, understand each other's mood swings and reasoning but, as in all good relationships, they have lessons to teach other.
Traditionally over the last 40 years, the Doctor has been the hero and the companion is a bit vulnerable. But here we've got an equal - we've got a hero and a heroine. She saves his life later in the series.
She's as brave and courageous and intelligent as he is.
Daleks - are they the most scary monster? Or are there worse?
In episode eight, there are creatures called the Reapers - they terrify me. The Slitheen are pretty frightening and there are the Gelth, and Cassandra from episode two. But for me, it would be the Reapers.
What's terrifying about them?
They fly and they plunge down from above. They're allowed on to planet Earth because there's been a break in time. It's like a wound in the natural order of things and they slip through.
And the Daleks - they're frightening. Not in the way they look - as they look quite old-fashioned - but the psychology is very frightening - they're the Doctor's Achilles' heel and they know all about his history and they are able to understand the way his mind works.
So it's the psychology of Daleks as much as anything - apart from the fact they want to take over the world!
So what's this going to do to children?
Terrify them, I hope! And move them and entertain them. The Doctor's really concerned that people accept other life forms, regardless of colour or creed. If he's got a problem, he will always think of some curious way to approach it. He just loves life - hopefully it will encourage children to love life.
How many times does the Doctor save the Earth?
There are 13 episodes, three two-parters, so I suppose I save the world 10 times before bedtime!
If you could travel back in time where would you go?
I'd go to Salford in the 1960s, when I was born, to meet my mum and dad and my brothers when they were very young.
Or I'd go back to the Salford of my mum and dad's childhood, and meet them as children.
I'm very interested in Salford - to see the places that I came from, that have influenced me throughout my life. I'd like to see my dad walking down the street.
Doctor Who is on BBC One on Saturday evenings at 7pm.
And don't forget there's a special Newsround Showbiz all about Dr Who at 3.50pm on Saturday, 26 March.