Comedy gold: Robin Williams's A Night at the Met

Title: A Night at the Met

Date: 1986

The setup: They'll never make a movie about the life of Robin Williams, eventful though it's been, because they'd never find another actor who could play him. He first came to prominence as the alien Mork in Mork and Mindy, and he's never since been wholly convincing as a human being. The speed of him, the way he just attacks performances with everything he's got, and with such skill, you watch him in the frame of mind you'd usually deploy for an awesome freak of nature like a solar eclipse or the Grand Canyon. It just doesn't seem possible for one man to contain so much talent and ebullience.

He's known as a great improviser – perhaps the great improviser – who invented a healthy portion of his Mork and Mindy scripts on the spot, and who continues to invent things at every opportunity. Indeed it's hard to imagine anybody memorising a show like this. There's just too much in it to do articulately, and it moves too fast. As he settles into things, it's clear that Williams has brought some structure, and a bag of good lines, but much of it is delivered almost in a trance. What it isn't, by any means, is a "routine".

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Funny, how? On paper, this is quite a conventional standup comedy show. Williams makes observations about being drunk and having sex, he gives his opinion of the president of the day (Reagan; not good), he decorates proceedings with a range of voices and improbable situations, slaloming around some readymade good lines. (Such as: "I realised when I became a reformed alcoholic: Hey, I'm the same asshole, I just have fewer dents in my car!")

In practice, most of this gets lost beneath the foaming torrent of his virtuosity. He is an incredibly graceful mover (and makes good use of the Met's enormous stage). He sings as handily as he impersonates, and can switch between them in a millisecond. His brief impression of silent movie footage is so fast that it makes you want to check the video for trickery.

Meanwhile, the associative drifts – from geopolitics into springtime into sex – are dizzying. You may realise that somewhere inside the scenes of heavily armed Californian households and polite British bobbies and machine-gun-equipped-cars and deer in armour plating is a commentary on gun control, or you may not. It doesn't matter. Nobody has come here to take notes on policy.

For sure, Williams has made some very annoying movies, in both his noisy and his quiet modes, but he himself says that he prefers live performance. If his thespy style of standup isn't to your taste – and it has got a little musty since 1986 – try just being astonishing by the spectacle. Before long you'll be washed away, laughing as you go.

Comic cousins: George Carlin, Lee Evans, Groucho Marx, Steve Martin.

Steal this: "Ballet: men wearing pants so tight you can tell what religion they are."