If Tom Hanks had listened to his dad, he would have a steady job by now. Like many fathers, Amos Hanks often lectured his son, trying to help him to navigate the tricky adult waters that lay ahead. There was one time, for instance, when Hanks Sr urged his son to get on down to the local Jack-In-The-Box, a fast-food restaurant, pretty damn quick because they were recruiting counter staff.

"In high school I had absolutely no drive or talent for anything that my dad was good at," Hanks recalls now. "My dad was good with tools, I wasn't. My dad worked in the restaurant business and I didn't really want to do that. I remember I was in the shower once getting ready for school and I didn't hear the bathroom door open and the next thing he rips the shower curtain open and says, 'They're hiring down at Jack-In-The-Box!' And I'm taking a shower, so I'm naked, and I'm like, 'Uh, dad, why would I want to take a job in Jack-In-The-Box?' And he says, 'Aw hell, any idiot can make assistant manager in six months!'"

Hanks tells this story with a smile, mimicking his father shouting, waving his arms around and pointing. We are sitting in the best hotel in Cannes, where he is arguably the biggest star at the film festival - his latest film, The Ladykillers, is in competition here - and the bizarre image of a young Tom Hanks serving up cheeseburgers and asking, "Do you want large fries with that?" is hard to overcome.

Fortunately, Hanks's own ambitions for himself were always far greater than those his father held for him. Thanks to the encouragement of teachers - he famously thanked one, Rawley T. Farnsworth, in his speech when he won his first Oscar for his role as an Aids-stricken lawyer in Philadelphia - he ended up doing what he always wanted to do: act. And much to the amazement of his father, he's done rather well at it. "Neither of my parents did anything like this," he says. "But they would come and see me in a play or something and say, 'I don't know how you do that, but great job.' And that was enough for me."

Even if he didn't admit it to Amos way back when, he felt the thrill of performing in front of his family, and instinctively knew it could lead him somewhere, at the very least out of Oakland, California, where he went to school.

"I was never an introverted kid. There was a time, I was nine or ten, and I got up and I made someone laugh and it was like, 'OK, that's it. There's nothing better than this.'"

He had an unsettled childhood. His parents divorced and he stayed with Amos, who remarried twice, and there were numerous homes in different small towns in California, and lots of stepbrothers and stepsisters. It must have had a profound effect, although these days he is able to look back and, mostly, laugh about it.

"I probably take what anybody else takes from their childhood," he says. "A certain amount of what not to do as well as what to do. You know, I'm closer with my mom now than ever before. And I guess that's because time has passed. I've got four kids of my own and I can see myself reflected in them. But at the same time I can see them not having to deal with any of the stuff that I had to deal with."

That "stuff" would have been the upheaval of moving, trying to make new friends, the devastation he felt over his parents' separation and, often, a crushing loneliness. Hanks has always been good at portraying isolation, because it's part of him.

As far back as Big in 1988, a comedy with some deceptively deep themes, he was breaking hearts as a 12-year-old boy trapped inside an adult's body. In Forrest Gump - which won him his second Oscar - he played a simpleton with a knack of succeeding the All-American way (war hero, millionaire businessman, table-tennis champion). But his mother (played by Sally Field) knows, and so do we, that Forrest is going to need someone to look after him because really he's a vulnerable little boy. Ron Howard's excellent Apollo 13 is almost unbearable when it seems as though the astronauts - Hanks plays Jim "Houston we have a problem" Lovell - will be stranded in space. The loneliness is crushing. And Cast Away, of course - which was Hanks's idea in the first place - is entirely about loneliness, with Hanks playing the only survivor of a plane crash washed up on a desert island.

"When I was young and trying to figure out what to do, I worked with Vincent Dowling [the Irish director] at a Shakespeare festival and I remember he said, 'Look, all the great plays are about loneliness, all the great stories are about loneliness. Richard III

is a lonely man, so is Hamlet.' And it's universal. It's in everyone.