Sitting down with Robin Williams is like being treated to a personal stand-up show. Although he can be considered and focused, it's almost as if the comic and actor can't help himself, inevitably riffing on anything and everything from marriage to the new iPhone. His comedic genius is evident as soon as he opens his mouth. This is a man who could probably develop a gut-busting routine based on something as innocuous as a doorknob.
Not surprisingly, the buzz among entertainment journalists is that Williams is notoriously hard to interview. He can barely keep a straight line of thought going for more than a few sentences, while the interviewer, it must be said, has trouble keeping a straight face. Generally, a 20-minute chat with him devolves into a rampant use of profanities on his part, and uncontrollable giggling from anyone who happens to be within earshot.
That said, Williams was in a slightly more sombre mood recently (well, for a short while, anyway). He turned to talk of rehab, God, religion and alcoholism - all of which have been close to his heart lately.
'You get a real strong sense of God when you go through rehab,' he says. Williams, 56, checked himself into a rehab facility in Los Angeles for about a month last year. His spokeswoman at the time said he'd been sober for 20 years, but then 'found himself drinking again, and has decided to take proactive measures to deal with this for his own well-being and the well-being of his family'. A year on, he says he's come out of it a better man. 'Having the idea of a really loving and forgiving God really helps if you're an alcoholic - someone going, 'It's OK. Remember, there was wine at the Last Supper.''
Williams, who was born in Chicago but moved to San Francisco as a teenager, says religion was an integral part of his childhood. But having just gone through rehab, his perspective has changed.
'It's become much more personal to me,' he says. 'Instead of my mother saying, 'We're going to church now', there's much more a sense of [religion] coming back to life for me. As a child, I was heavily into religion. I was into the ritual of it. I'm Episcopalian, which is Catholic Lite - same religion, half the guilt. I grew up in San Francisco where the gospel music is so beautiful. I'm more religious in the sense of an open, compassionate church that's there to take care of people with outreach programmes and counselling. The idea of really working together, that means something. I'm religious on that level, trying to take care of every- one, and the idea of compassion is powerful to me.'
He fell back on his faith during his recent struggles with drinking, which he described as being 'one of the coming attractions of hell'.
'You have an idea there's a dark force when you're in that space, and it's totally the opposite of doing the right thing.'
He believes in the afterlife - but can't resist making a crack about it. 'You talk to people who have had those experiences and it's always a white tunnel and you realise, 'What if it's [New York's] Holland Tunnel and you're just going to Brooklyn?'
Williams' latest film is License to Wed, a romantic comedy co-starring Mandy Moore and John Krasinski, who's better known for his role in the hit comedy series The Office. The film has been savaged by critics, was a flop at the US box office and was shelved from release in Hong Kong cinemas. Nonetheless, Williams, with his earnest eyes and ready smile, was perfect for his part as the Rev Frank, a well-intentioned but over-the-top head of the local church whose job it is to counsel prospective brides and grooms. 'His character gives advice on human sexuality, which is kind of like Quasimodo at the chiropractor.'
Williams has been married to his second wife for 17 years and has three children. What has it taught him? 'I've learned about honesty. And I've learned about the idea of being straight with each other, to be OK with the fact that you can't manipulate and change some- one. You want to say, 'Thanks for accepting who I am, because I'm a piece of work. Marriage is a long programme, hopefully. Except in Vegas, when it's 'I do, I don't, I do.''
He can't resist having a jab at the state of matrimony, a subject that, in his hands, is caustic but funny.
'In the beginning, you want to rush headlong into it and yell, 'I love you!' And then, after a while, it's 'I love you' and after a while more it's 'What the f*** are you doing here?'. Later on, it's 'What's your name?' That's the alcoholic's worst nightmare, when you wake up and say, 'Who are you?''
He then turns serious again.
'I think anything that people can learn about each other before they get married is a good thing. Anything that puts you through a test, that helps you problem-solve.'
And then, the riffing again: 'You put [prospective couples] on an island say, 'Find food, you have two hours'. And you'll find out the women can do it, and the guys go, 'What? If I can't kill it, I don't want to know it. If I can't fight it or f*** it, I don't want to know it. The women will say, 'We need to go gather, we need a nest,' and the guys go, 'A nest? Can I s*** in the nest?''
The comedy of Williams is a Hollywood institution. The highly animated actor burst onto the scene in the late 1970s with his hit show Mork and Mindy, in which he played an alien. He landed the part by walking into the audition, and sitting on his head in the chair.
Until then, he was one of many struggling comedy actors waiting for a break. He had sidelined his interest in political science to study theatre at the Juilliard School. After graduating, he went straight onto the stand-up circuit. He first played Mork on an episode of Happy Days.
From there, he's worked his way up to Hollywood's A-list, seguing from brilliant stand-up shows to hit films such as Good Morning, Vietnam (1988), for which he got his first Oscar nomination.
He was nominated again for Dead Poets' Society and The Fisher King and returned to his comedy roots in the family-friendly Mrs Doubtfire. He lit up the screen with his fey father role in The Birdcage, and finally went home with the Oscar in 1998, for his role in Good Will Hunting. But some of his choices have landed with a thud at the box office - and in the eyes of reviewers. What Dreams May Come (1998), for example, won awards for best visual effects, set decoration, art direction and production design - but, as one critic said, 'How could one take Robin Williams seriously?'
And of Patch Adams, in which Williams plays a doctor who uses humour to treat patients, one reviewer wrote scathingly: 'Somebody needs to come up with a remedy for the maudlin Robin Williams comedy.' Indeed, for a while, 'maudlin' appeared to be Williams' middle name - until he broke through with roles as pathological villains in films such as Insomnia and One Hour Photo.
But he loves comedy, and says he particularly enjoyed Knocked Up and Hot Fuzz. 'I think these new comedy films are great. They're new and crazy and they push the envelope, like they should. They're designed to come out and smack you right between the eyes.
'Good comedy addresses real issues in outrageous ways, and without language or behaviour boundaries. That's what it should be, and that's what makes me laugh.'