Why is "Doctor Who" the greatest TV show ever? Steven Moffatt can tell you why: because of the lives it's touched and the people it's inspired.

"Who" writer and producer Moffat grew up a fan of the long-running time-traveling adventure before taking charge as showrunner in 2009, shepherding the series through its 50th anniversary. He bid farewell to the show on Wednesday night at a screening of the forthcoming Christmas episode, "Twice Upon a Time". That'll be the final episode for both Moffat and current Doctor Peter Capaldi, with new star Jodie Whitaker appearing in the closing moments.

"I've seen a tiny bit of Jodie," Moffat hinted, "and she's absolutely amazing."

Capaldi wasn't present at the screening at London's Science Museum, but he did send a message thanking his friends on the show and wishing Whitaker good luck. Capaldi also saluted Moffat, who the actor said has "brought so much to 'Doctor Who' -- even more than might be realised today, but will be seen clearly in the future."

I was in the audience with other press and fans, watching the episode and transcribing a question-and-answer session with Moffat and the cast. But as the Q&A came to an end I had to stop typing and just listen, the hairs standing up on the back of my neck, as Moffat said this:

"It is actually the greatest television show ever made. There are press here who'll say [affects sneering journalist voice] 'Oh, it's 'The Wire''.' It's not 'The Wire'. It's not 'I Claudius'. It's not 'The Office'. It's not even 'Blue Planet'. I'll prove it to you. How do you measure greatness? Do you measure it by ratings? Do you measure it by reviews? Christ no. Do you measure it by perfection? Is 'Doctor Who' perfect every week? It really isn't. It can't be. Every episode of 'Doctor Who' is an experiment, and if you experiment, sometimes you'll get a faceful of soot and you're blinking the smoke away and you look a bit ridiculous. 'Doctor Who' by always being different can never be perfect. How do we measure its greatness? There are people who became writers because of 'Doctor Who'. Loads of them. There are people who became artists because of 'Doctor Who'. There are people who became actors because of 'Doctor Who'. Two of them have played the Doctor. There are people, believe it or not, who became scientists because of 'Doctor Who'. That seems improbable given we said the moon was an egg ... but people become scientists, people change their view of the world and what they're capable of, because of a silly show about a man who travels around in time and space in a police box. So never mind the reviews. Never mind the ratings. Never mind any of that. Count the scientists, the musicians, the scholars, the writers, the directors, the actors, who became what they are because of this show. Count the hearts that beat a little faster because of 'Doctor Who'. I do not even know what is in second place, but by that important measure 'Doctor Who' is the greatest television show ever made."

Cue thunderous applause from the audience of "Who" fans.

Tommaso Boddi

One devotee who became a writer, actor and director is Mark Gatiss, who also appears in "Twice Upon a Time".

Admitting he was "in pieces" watching the episode, Gatiss described the shoot as a roller coaster of emotions. "We had a good laugh and then it got increasingly tinged with sadness," he said. "Peter said 'that's the last corridor I'll ever run down', and things like that. But overall it was a joyous thing.

"I think everything brilliant and beautiful about 'Doctor Who' is in that episode," Gatiss added. "It made my heart sing." Then he started welling up again, and he probably won't be the only one.

"Twice Upon a Time" airs on the BBC on Christmas Day.

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