The new “Doctor Who” is broadcast during Britain’s family friendliest hour  just after dinner on Saturday nights  and it too has morphed into something else altogether, science fiction that is playful, sophisticated, emotionally resonant and peppered with lightning-quick allusions to literary works, to classic “Doctor Who” episodes from long ago, and to historical events and people. But Mr. Davies presses his grown-up themes with a whisper and a laugh, not a shout. No one actually has sex on screen in “Doctor Who.” And when Captain Jack makes an appearance (only rarely, since he now has his own show), his sexuality is an issue only in that his constant, equal-opportunity flirting tends to annoy his colleagues, busy as they are fighting intergalactic evil.

“He takes ‘Doctor Who’ and pushes the envelope the whole time, not in terms of taste and decency but in terms of ideas and emotional intelligence, the size of feeling and epic stroke of narrative breadth,” said Jane Tranter, the BBC’s head of fiction. She said that no one at the BBC had ever had a problem with Captain Jack or with any of Mr. Davies’s plotlines. “How ridiculous would it be that you would travel through time and space and only ever find heterosexual men?” Ms. Tranter said.

Hiring Mr. Davies to remake the beloved but, finally, creaky old series was a daring, even counterintuitive move by the BBC. First there was the worry that “Doctor Who” had already had its day, that it belonged to another era altogether. But more than that, Mr. Davies was a risk taker with no obvious science-fiction credentials other than a fanatical lifelong devotion to “Doctor Who” and a headful of ideas about where to take it next. At the time, in 2003, he was best known for “Queer as Folk,” a 1999 series that chronicled the lives of a group of hedonistic gay men in Manchester with a frankness never shown before on mainstream television. (It was later remade in the United States.)

“Queer as Folk” was revolutionary not only because of its racy subject matter but also because of the matter-of-fact way it presented its characters: ordinary people, if unusually attractive and sexually frisky, who happened to be gay. Criticism of its content tended to be overshadowed by admiration for its wit and verve and for the mature fun of its story lines. Mr. Davies used the same philosophy when Captain Jack came on the scene in “Doctor Who”  make it entertaining, not didactic.

“I thought, ‘It’s time you introduce bisexuals properly into mainstream television,’ ” he said, laughing.