Thank god I can stop defending Matt Smith after Saturday's triumphant Doctor Who.

I interviewed him 18 months ago when he was on stage in That Face, and knew he was really special. Smart, unpretentious, he can actually talk to women in their forties, a rarity among young actors. And he's completely unvain – as anyone who saw him wearing a urine-soaked dress in That Face will testify.

But the last month has been exhausting, telling worried fans: "No honestly, he's going to be great. Steven Moffat knows what he's doing." Moffat, like the great Russell T Davies before him, knows you find the most interesting performers in odd places – mostly gritty fringe theatres. You cast the one who seems most unlikely, with problem hair and gangly limbs, and whoosh the blue touch paper is lit.

The funny thing is I was never a Who fan. Too male, too anoraky. Who really cares about sonic screwdrivers? But when Russell T came in, and cast Christopher Eccleston in 2004, I took notice. Eccleston, a great, intense actor, told me excitedly that the new show would be aimed directly at 10-year-old girls. Hence the casting of Billie Piper as Rose.

"Russell's thought: how can I get girls into it," Eccleston explained. "And he's given them a proper heroine. The Doctor will be quite sidelined at first and it's like revenge for 40 years of domination. If you look at all of Russell's work, his particular strength and interest is women. He writes gay men brilliantly, but is not especially interested in heterosexual men. Everyone else is, so he doesn't bother."

Of course when Doctor Who goes wrong for actors, it does so spectacularly. Eccleston, so enthusiastic, quit before the first series had gone out (there's still a story to be told). Paul McGann was an inspired choice in the Nineties, but the scripts weren't good enough.

Trillions of fans have an intense love-hate relationship with the show. So even when it works it can be a poisoned chalice. Peter Davison told me it took years to convince casting directors he could play proper character roles (go and see him in Legally Blonde and marvel). Tom Baker was finally rescued by Little Britain.

Eccleston spent time in the wilderness (but will be back in a BBC4 drama about John Lennon). And even the fabulous David Tennant has seen his mooted US TV series put on hold.

I admit I'm totally the wrong sort of person to write about Doctor Who. Sci-fi leaves me slightly cold. But the brilliance of the last three incarnations of the Doctor is indisputable. The scripts are politically charged; and Russell T has given the cream of the theatre world (Penelope Wilton, Claire Bloom) careers for life.

Yes, I'd have liked a woman this time. Judi or Tilda would have made history. But actually Matt Smith is perfect – because he has that boy-girl thing going on.

For the first time ever we understand what it must be like for the Doctor to inhabit an entirely new body. And frankly the standout performance on Saturday was, yes, a 10-year-old girl. Caitlin Blackwood as the young Amy took your breath away. She'll be the new Time Lord in 12 years' time.