Robin Williams has been the eternal Lost Boy of movies but, in his latest film, he has rediscovered the grown-up actor within. By Martyn Palmer
If Robin Williams finally manages to win the Oscar that has eluded him on three previous occasions, he promises that his acceptance speech, in front of a global audience of billions and a local Who's Who in Tinsel Town, will be short and to the point.

"Yeah, I'd like to win," he admits. "I'd like to pick it up and go 'look, Oscar has no balls!' I've lost three times and it's so much fun to go along and go 'grrr! Oh, somebody else won? Oh good for you... la la la...'."

Not that Williams is counting his chickens, you understand. But his performance as a world-weary, troubled shrink in Good Will Hunting is attracting plenty of smart money in the Best Supporting Actor category.

Indeed, it's a role - unlike some of his over the top and frankly disappointing film outings of late (Jack and Father's Day spring to mind) - which reminds you that there is a serious actor lurking beneath that manic, madcap exterior.

His three previous nominations came with Awakenings, The Fisher King and Dead Poets Society and, with Good Will Hunting, Williams is once again reigned in - by director Gus Van Sant - to a point where, in his terms, he is positively understated.

"For a while I was trying to look for movies, it was like 'this is your academy award winning movie!' But if you do that, it's like trying to kiss your own ass - you can't do it. I'm not that flexible.

"Now I just try and find movies that I enjoy making. You have to be willing to put your heart and soul into it, rather than trying to achieve some award that may not happen.Good Will Hunting was exactly that"

Yes, he can play the man-child with a degree of charm - notably in Jumanji, Jack and the recent box office success Flubber - and yes he can pack audiences in and "deliver" a blockbuster like Mrs Doubtfire. But it would be nice to see him do more along the lines of Good Will Hunting and Woody Allen's Deconstructing Harry which is to be released here soon.

Williams is slightly defensive when you ask why he chooses some of the films he has of late. Flubber, for instance, is a remake of the 1961 Disney classic The Absent Minded Professor and, says the actor, was unashamedly made for kids. And there's nothing wrong with that, he points out.

"I took my son to see the original as a result of being offered the part and he was laughing like crazy. So I thought 'this is a good sign'."

He has three children, Cody, 5, and eight-year-old Zelda from his second marriage to Marsha Garces - who at one point was nanny to his oldest child, and 14-year-old Zachary, from his marriage to dancer Valeri Velardi.

He describes himself as a "good father" and clearly the child inside of him - which informs so much of his work - is given free reign when he is with them.

"I play with them, yeah, of course I do. I mean I run around and get to be a kid again myself. It's like time travel, you get to go back in time and play hide-and-seek, or go to a science museum and have fun with them, and at other times you have to be more serious and be a grown-up father and give them advice.

"I'm a good father. But I'm a work-in-progress like every father. I think every family is dysfunctional, a functional family is like 'we are a functional family'. Who wants to be that? Rubber hose is functional."

He wasn't functioning too well when in the grip of a cocaine habit.

"I was kind of lost and a bit like Freud's grab-bag", he says. "You know, I played a character in a film a bit like that last year (Father's Day). In that, I find out that I had a kid that I didn't know about and it suddenly gives the character a sense of purpose. And that's exactly what it did for me.

"And I did it in a rat's second. Before that I was a member of the Columbian fund and I didn't want to be like that with my son. You know, like five in the morning 'HEY, YOU WANT TO COME AND PLAY WITH DADDY? OH, LOOK AT THE TOYS, LOOK AT THE TOYS!'

I couldn't be like that with him, whacked out of my mind shouting 'DADDY LOVES YOU!' So I stopped. I cleaned up."

As a bright, academic teenager, there were no signs of the humour waiting to burst out, he says. Instead he embarked on a political science course.

"I loved languages and I was heading for a career as a diplomat. I would have been in an embassy right now. It's a frightening prospect, isn't it?" he laughs. "I think you could say that I found the right profession..."

Then he decided to enrol for an improvisational theatre class. It was, he says, one of the defining moments of his life. "I was in the right place at the right time with the right teacher, who was this wonderful woman who inspired me.

After a year he left and won a place at the prestigious Juilliard Theatre School in New York and from there began to work as a stand-up comedian.

He believes he inherited his sense of humour from his mother. "She has a very strange sense of humour," he says. "She's very funny - like a combination of Neil Simon and Dostoevsky.My father was a very elegant man, a very ethical man and making Father's Day brought back a lot of memories of him. I thought about him a lot and what he meant to me.

"He was one of those fathers, like a lot of fathers in the Fifties and Sixties, who worked their asses off and they weren't always there because they were away working. But the nice thing was that I did get to know him later and he was wonderful, a really nice man. And that was great - it saves you years of therapy."

Therapy is something that Williams has experienced himself. "The truth is you do better work the more comfortable you are with who you are. You can comment and explore different things rather than always trying to cover it up. You can also keep it separate and create a character without always having to be like 'this is me!' It's been a good thing for me to do over the years, really good."

Perhaps his own experience of therapy helped him with his role as Sean McGuire, the bruised and battered college professor and therapist who has tried to survive his own emotional upheaval (the death of his wife) and attempts to help the young Will Hunting (Matt Damon) overcome his own demons.

Once he had read the script, Williams hardly needed convincing that this was a role, professionally speaking, to die for. He shifted projects in an already crowded schedule so that he could work with Van Sant - a director whose films, including Drugstore Cowboy and My Own Private Idaho - he greatly admired.

"Good Will Hunting is a battle of wills," he says. "It's a love story with four different parties vying for Will's soul. There's so much going on in any given scene, it's layered in many ways and was a joy to work on."

Perhaps one of the best things about his performance in Good Will Hunting is that he didn't get to play a child. In this film at least, Robin Williams is all grown up.

'Good Will Hunting' opens today