The star behind Spider-Man

Until he donned the blue and red stretchy suit and became Spider-Man, Tobey Maguire's stock in trade as an actor was playing the geek.

When you meet him, you can see why. He is small, a bit bug-eyed and he talks in a strange robotic monotone, like a sixth-former reciting a newlylearned chemical formula. He is also (and this is the annoying part) a smarty-pants. He never indulges in false modesty and he delights in giving silly, opaque answers to the most mundane questions. Grilling him was like interviewing Confucius: the man from LA, he talk in riddles.

But at almost 27, and nerdy manners apart, Maguire is a bona fide movie star. Although he had to audition for Spider-Man - the studio was not quite as sure as the director, Sam Raimi, that Tobey would make a convincing superhero - he has proved to be worth his weight in gold. In the United States, 20 million people went to see the film in its opening weekend.

For a man more used to starring in understated movies such as The Ice Storm, this exposure must have been a shock - which is, perhaps, why his behaviour has been so surly. At the Spider-Man premiere, he apparently got in a huff when he was rained on, snarling at autograph hunters that there was "no way" he was signing anything.

So has it been difficult not letting all the attention go to his head? "No," he says, dangling one of his trainers on the ends of his toes (we are sitting two inches apart on a sofa in the Dorchester). "I think it is easier not to let it go to your head. I think it is an actual effort to let it go to your head." Can this be true? He slows his speech, as though he were talking to a child. "Well, let's say a situation happened where you were getting tons of attention. Maybe you'd enjoy it. But, at the end of the day, the foundation of your life is you. You're not your fame or your material possessions."

Even so, people must treat him differently now that he is a megastar. "I guess they notice me more." What about girls? Although he is rumoured to have dated his Spider-Man co-star, Kirsten Dunst, and was recently photographed with Nicole Kidman, he is supposedly single. Are they more interested in his fame than his, er, personality? "I think you can always tell if someone has an agenda. One little comment can inform you of their position."

So who helps him to keep his feet on the ground? "I give the credit to everything and everyone. I just mean, like, the universe. If I got out of hand - which is laughable to me, but if I did - my friends would go: phrrrh!" He blows air through closed lips so that he sounds like a horse. "They wouldn't even find that kind of behaviour worthy of a comment." He makes the horse sound again. "Phrrrh!"

Well, I say, perhaps his friends - who include Leonardo DiCaprio and the magician David Blaine - are just too famous to notice when someone is obnoxious. "Most of my friends are not famous," he says.

"I only know a couple of people who are."

OK, so what about money? Maguire has known poverty - his father was a cook, his mother was a secretary and, after their divorce, he spent his childhood shuttling between the two - but now he is set to make $26 million from two Spider-Man sequels. Has it been hard adjusting to having so much cash in the bank? "I don't go spend, spend, spend," he says. "I live below my means so I don't have to go back to a place where I don't have money. I'm not extravagant, I don't like shopping, except for CDs and DVDs." So far, his biggest purchase has been a house (it's in Los Angeles, although he won't tell me where, exactly, or even if it has a swimming pool).

Maguire started acting at the age of 11, when his mother bribed him with $100 to take drama instead of cooking classes. At 14, he dropped out of school and began going to auditions. At 20, he got a part in The Duke of Groove, a short film which was nominated for an Oscar; Ang Lee saw it and cast him as an angst-ridden teenager in The Ice Storm. "I always felt I would be a success," he smirks. "I'm hungry, I'm a hard worker, I don't limit myself, I don't let psychological road blocks get in the way."