As a long-term fan - all my life really - it's hard to explain the excitement the very first time I typed the sentence "The Doctor opened the door of the Tardis." It's just such a thrill to get to play in that sandpit.
I will say, writing for a 'real' person - at least, someone with a physical existence - is very different from writing my normal novels, which are peppered with people from my own head. We all know what the Doctor sounds like, and how he acts and it's quite strange to work like that for a novelist. Recently I had written a scene for Matt Smith for something, then it had to be changed for David Tennant's Doctor. I couldn't keep a single word the same. The way they talk, the way they move, the interests they have are so completely different; it's fascinating to play the game of literary ventriloquism, and nothing pleases me more than when people tell me I've successfully caught the Doctor's voice.
I grew up with Tom Baker and Peter Davison playing the Doctor- when I was eleven I won a competition to meet Peter Davison in London. It was very exciting. There weren't a lot of female fans then, and I had very short hair and was wearing trousers and sandals, and Peter called me 'son'. I think he thought I was a boy. He also told me not to look inside the plywood Tardis as I would be "very disappointed". He was wrong. Everything about the experience made me more of a fan than ever. As a little coda to that, I read an interview with David Tennant, who's my age, a few years ago, and they asked him if had always been a fan of the show and he said: "Yes, when I was eleven I entered a competition to meet the Doctor. I didn't win though..."
I've loved all the new Doctors. I loved Christopher Eccleston's steely strength, and DT's manic energy, and I love how alien Matt Smith is. From the second he appeared he looked utterly like he was from another planet.
It is sometimes a little odd being a girl in the Whoniverse, though not as much as it was when I was eleven. Male Who fans try and catch me out sometimes, as if I'm trying to pass myself off as something I'm not (which would seem a really odd thing to do). And I'm probably more interested in the Doctor's emotional hinterland than the monsters. What's fascinating to me is that I often feel the Doctor's traveling is, to him, not terribly important, or at least, it's only a part of what he is. All the really interesting stuff about him - his name, his family, his upbringing, his children, how he thinks what he thinks - we'll never ever know about, and that makes him endlessly fascinating to me. Well, that, his blue box, his friends, and the whole of time and space. It really is the most tremendous sandpit.
Doctor Who: Dark Horizons by J.T. Colgan is published by Random House UK.