An e-mail from Russell T. Davies - my terrific showbiz pal - notes that, in Wales, the fact that he has just stepped down from Doctor Who has made the evening news.

“The NEWS!” he boggles, before adding, ruefully, “Though the next headline was, They Still Haven't Moved That Skip.”

And Davies's departure isn't just headline news in Wales. It is news that reverberates across all space and time, from Raxacoricofallapatorius to the end of the Universe and back again. For this isn't just the resignation of a writer and executive producer on a children's TV show. This is the resignation of the 15th most important media player in Britain, as calibrated by The Guardian last year. This is the man who resurrected a piece of British heritage, a key part of our mythology. For Russell T. Davies brought Doctor Who back from the dead, and made this country's playgrounds ring once again with “Exterminate!”, “Get in the Tardis!” and “If you don't let me be the Doctor this time, I won't be your friend.”

It's hard to believe now, when Doctor Who is to all intents and purposes the BBC's flagship show, but when Davies first suggested bringing back the Doctor he was considered totally barking. In 2003 he had just won the Royal Television Society Award for The Second Coming - Christopher Ecclestone as the new, Mancunian Messiah - and was still surfing off the success of his taboo-busting and hootingly funny gay drama, Queer As Folk.

Born in Wales, educated at Oxford and settled in Manchester, Davies had made his reputation by taking ostensibly controversial subjects - gay relationships, a new messiah, omnisexual historical adventuring (Casanova), Jonathan Creek going gay, then straight (Alan Davies in Bob & Rose) - and proving that they could make accessible prime-time dramas so long as you wrote the whole thing with joy, wit, tenderness and a fierce line in philosophical relativism.

So when he used his newfound professional leverage to resurrect Doctor Who - a show remembered primarily for its 1980s decline into overacting, miscasting and monsters made of rick-rack - there was widespread derision - yet he turned in a masterclass of creative reinvention.

Sometimes, with its cutting-edge FX, Doctor Who is the dystopian sci-fi nightmare of your childhood. Cybermen! Flying Daleks! Skies full of attack ships! And at other times, with its beautifully weighted relationships and ebullient good humour, it's like Coronation Street in space. Its success has been phenomenal, and Davies leaves the show as a writer who could get any project, no matter how ostensibly ludicrous or costly, green-lit.

“But to be honest, every other job in British TV feels so small, after this job,” he concluded in his e-mail last night. “I might try running ICI instead. Or KFC. I love KFC.”

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