JAMES GANDOLFINI, the lead actor in The Sopranos, has long been used to the unsettling experience of meeting strangers on the street who momentarily rock back on their heels with expressions of fear. He remembers opening the door of his home to a man one evening and watching as the blood drained from his face. These are the people who confuse reality with fiction and wonder if they are about to be whacked.

If pressed, Gandolfini, who at 45 has achieved enough in his career to take early retirement, will admit that he shares some of the character flaws of Tony Soprano, the conflicted New Jersey mob boss he has played with such intensity for almost a decade since the show premiered on HBO in the US in 1999. But there are differences, of course.

Murder is not on his CV, nor bone-breaking nor loan-sharking. Nor has he ever been shot.

My own meeting with Gandolfini occurred several years ago when I happened to be on the Silvercup Studio lot in Queens . . . not, happily, in a dark alley . . . where he and the cast were in the midst of shooting the second season. The door of his trailer swung open and out he stepped, all 260lb of him, attired in Tony's favourite white dressing gown and giant slippers. He squeezed my hand, delivered a disarming smile and vanished upon discovering that a reporter had penetrated the set.

Modest and self-deprecating Gandolfini has never much liked giving interviews. Everything about him . . . his sheer size and the phenomenal applause earned from his years playing Tony . . . would suggest a man who could afford to swagger a little in the spotlight, especially with the final season of The Sopranos poised to begin tonight on American televisions. Yet the truth about this one-time club manager and son of bluecollar parents in New Jersey is that he is entirely modest and often self-deprecating.

It is a trait that surfaces when he speaks of other actors whom he usually seems to admire more than himself. In a recent interview, for instance, he fell over himself describing the ability of his co-star in the film Romance & Cigarettes, Kate Winslet, to talk dirty during their sex scenes.

"I was very impressed with how much stuff she could make up about sex. I remember being underneath Kate and she was chatting away; she kept going and going and going. I was thinking, 'God, I hope we stop at some point!' Every time she'd make up new stuff, the director would say, 'Keep going!'

And she went for it."

Certainly, he was astonished when he was originally approached by David Chase, creator of The Sopranos, to star in the pilot so many years ago. His career until then had not been stellar. "I thought, I've never been the lead before. They're going to hire somebody else, " he told Vanity Fair. "But I knew I could do it. I have small amounts of Mr Soprano in me. I was 35, a lunatic, a madman." Even when they began work on the pilot, Gandolfini did not allow himself to imagine the show would work. "I looked around this group of fat, ugly guys and said:

'Let's do the pilot and go home!'" The rest, as they say, is television history. The Sopranos established itself as must-see Sunday night viewing for millions in America and in countries around the world where HBO sold it. At the core of its success were Gandolfini and the programme's team of writers. In Tony Soprano, who famously spends as much time in the office of his psychiatrist, played by Lorraine Bracco, as in the company of his crooked crew, they created a character who was devoid of moral standards and yet also tortured and thus irresistibly sympathetic.

A "lovable, huggable murderer" is the best description Robert Thompson, head of Syracuse University's Centre for the Study of Popular Television, can find for Tony. "This was a show that demonstrated how novelistic and how sophisticated television could be. It is not only about bad guys; it's about people who are at the heart, horribly, morally corrupted individuals. But at the same time, they were presented in a way where we really could identify with them."

Gandolfini himself has explained that it is precisely the challenge of exploring the deeper recesses of people that has fuelled his interest in acting throughout his career. Most appealing to him is representing the small guy from the same background he came from, working class. He is captivated also by people who have had troubled periods in their lives, as he has.

"People really interest me, especially the way things affect them, " he told one interviewer. "It's basically why I became an actor. I have this big passion for the lower middle class and the blue-collar guy. It's how I was brought up, and I don't like the way our country treats them. By becoming an actor, well, I found this job that lets me, on occasion, stand up for the blue-collar guy, in a small way."

Born near the Jersey shore, Gandolfini was the son of two Italian-Americans . . . Michael, a bricklayer and school maintenance man, and Joann, who worked in a school kitchen. "My father always said a million times, 'We're peasants', " he once said, which partly explains why he is press-shy. "It's just a little odd for me, to get that slightly different treatment sometimes. And I'm uncomfortable with it.

I want nothing to do with privilege."

After studying communications at nearby Rutgers University, he moved to New York where he worked as a waiter, a club bouncer and eventually went into club management. Serendipitously, he had a friend taking evening acting classes and one day he decided to go along. It wasn't long before he knew acting was what he wanted to do with his life.

By then he was already in his mid-20s.

Vomiting emotions Watch Gandolfini play Tony and you know that he has an ability to channel anger and emotion into his performances. Some of it, he admits, has been drawn from the well of his own life, particularly a tragedy at just 19 when his girlfriend of two years was killed in a car accident. "I might not have done what I've done" without her death, he told GQ, acknowledging that acting gave him the opportunity for release. He once said that acting allowed him to "vomit my emotions out of me".

There have been other points of turbulence in his life. A marriage to a former public relations executive, Marcella Wudarski, in 1999, with whom he had one son, Michael, ended in acrimonious divorce in 2002, just at the time that his celebrity as Tony Soprano made him perfect fodder for the tabloids.

Wudarski fuelled the fire with allegations in court of alcohol and drug abuse by her husband. Gandolfini has freely acknowledged having to battle substance problems and pulling himself together in rehab but declines to elaborate in interviews. In 2004, he announced his engagement to Lora Somoza, a writer, but the couple split two years ago.

Professionally, his first big break came with a supporting role in a Broadway revival of A Streetcar Named Desire alongside Jessica Lange and Alec Baldwin. Soon after, he landed his first film role in Sidney Lumet's A Stranger Among Us (1992), which was quickly followed by the part of the mob enforcer Virgil in Tony Scott's 1993 film True Romance. Other films followed, including Crimson Tide, also directed by Scott, as well as Get Shorty (1995), The Juror (1996), Lumet's Night Falls on Manhattan (1997), She's So Lovely (1997), Fallen (1998) and A Civil Action (1998).

That The Sopranos should so quickly have reached the heart of American popular culture astonished everyone, not least Gandolfini. "We were all surprised at the show's success, " he says.

"The work that he and David Chase have done in creating the character of Tony Soprano is one of the most interesting things in the history of television, " says Chuck Rose, who runs the annual Filmmakers' Symposium in New Jersey. As for any similarities between Tony Soprano and James Gandolfini . . . Jimmy to friends . . . Rose says, "He's the opposite of that character. In real life, he's a sweetheart, a teddy bear, and I can tell you that's extremely rare, from the actors I've dealt with."

The pleasure of watching Gandolfini playing Tony is almost at an end. Among his future projects is portraying a man of similar physical presence, Ernest Hemingway. We could wish he would reprise Tony a few times more, but every good performer knows when a character has run its course.

"I'm old, Carm, " he tells his wife in the first episode of the closing season, pausing to reflect on the gunshot wound that nearly killed him. "My body has suffered a trauma that it will probably never fully recover from. So why don't we just face the facts?"