Tobey Maguire: The boy behind the mask

Tobey Maguire is Spider-Man. In his new film, he's riding racehorses. But, discovers Roger Clarke, he's hardly the hero type

He's no pin-up but there's something about the physicality of Tobey Maguire - much more rangy, shifty and watchful in the flesh than you could ever imagine from his sweet-natured films - that always invites comment. Earlier this year, all the papers reported his alleged weigh-in with the makers of Spider-Man over his back problem (there is even talk he was about to be replaced for the just-finished sequel, which he denies); it seems that he was not entirely open about a long-standing herniated disc (something again he denies) which put the whole stunt-based nature of Spider-Man 2 in jeopardy. Well, everyone is talking about his back and his diets - his diet for Spider-Man, his diet for his new film Seabiscuit - in a way that's most unusual.

No other male actor his age has to put up with his food intake, waistline and exercise regimes being so scrutinised. Pictures of his paunch on a beach jostle with images of Cameron Diaz's spots in the gossip magazines. Then there's his carb-and-calorie intake, his yoga, his vegetarianism, his weight training - we could easily be discussing Demi Moore.

Maguire has always been an intriguingly passive presence, an amused man-boy, one that suffers and foments the fringes of the action in movies like The Ice Storm, Wonder Boys and The Cider House Rules. That all changed, apparently, with Spider-Man, which is now the fifth most successful film of all time; suddenly the sleepy young actor was in the thick of the movie's upfront physicality. The super-spider that bit him in the film and turned him into a muscle-toned, super-strong, web-slinging superhero might just as well have injected him with neat testosterone. Just on the verge of a career downturn - Wonder Boys was promoted without even mentioning his name - he stopped being a boy and became a man.

And yet the ambiguity remains. Although Spider-Man was a trenchantly macho role, Maguire's slightly feline scepticism shines through, like an unimpressed teenage girl, under all that filigree lycra. He still doesn't act like a grown-up, despite recent very grown-up revelations about his alcohol problem and his endorsement of Alcoholics Anonymous ("it has totally changed my life"). Though he smoked a cigar throughout the interview I had with him - and as a millionaire, of course, he's entitled to do so - at the grand old age of 29, he always looked exactly like a kid playing with smoking a cigar.

And then there's the height thing. Though no feisty bantamweight like Robert Carlyle, he's a short man, something that's been carefully disguised in his films till now (Hollywood has a whole science devoted to disguising the tiny physiques of its leading men). Michael Caine - who acted with him in The Cider House Rules - once churlishly mentioned Tobey Maguire as one of a diminutive current generation of young lead actors who are "more ambitious because they are more angry because they are short".

One senses his ambition, for sure, beneath that benign exterior, those sleepy eyes and those slightly billed lips. Seabiscuit is all about the ambition of the 1930s jockey Red Pollard, a man who struggled against a tough childhood and drinking problems, yet willed himself and his clapped-out steed to the top of the racing hierarchy. "I knew Tobey had lived a difficult life," says the director of Seabiscuit, Gary Ross, who wrote the part for him. "I knew he that had fire in him, a complexity and an innate toughness."

In fact, Maguire is quite happy to talk about his body, because he famously cuts short any enquiries into his personal life, and much of his routine observations about his films could have come from a PR booklet. After finishing with his 1500-calorie-a-day regime for Seabiscuit ("all you want is sugar - I had mini-breakdowns where I said bring me as much candy and doughnuts as you can possibly find") he switched to bulk-up for Spider-Man 2 ("you taper the carbs throughout the day," in case you're interested).

It's like Method, but not quite. "You look in the mirror and you start to see characters poking through the physicality, and that's fun," he observes, interestingly focusing on mirrors and character-pregnancies (as it were) and fun rather than the puritanical self-cleansing masculinity of De Niro or Pacino.

And we did talk about his back. You may remember the press reports from earlier this year - Maguire in trouble when he failed to inform the big shots at Columbia of a long-standing problem with back pain. One paper even suggested Maguire had been sacked in favour of Jake Gyllenhaal, though in fact this never actually took place, and was never on the cards. How was his back after all that horse-riding in Seabiscuit? "It was fine," he croaks. "It didn't aggravate my back any further and if I take care of myself I'm basically in no pain. I've had some discomfort over the years depending on what I was up to, playing lots of basketball and things like that. Not stretching enough makes it worse, and you have to build up your abdominals and your legs. The silly thing was that the back thing was blown out of all proportion. It's so common, the most common condition after the common cold". Were you born with it? "I'm not sure."

He had experience riding horses with Ang Lee in Ride with the Devil. "I love riding and I had the same horse-wrangler, Rusty Henrickson, I had on Ride with The Devil. Before him, there was this really old-style wrangler called Monty. And I said, 'Monty, is there anything I can do to advance me more quickly?' And he said, 'Miles, Tobey, miles.' You've got to put in the hours. Thank God I'd already learnt to ride, or it would have been very difficult." Maguire chuckles at the memory of this wise old-timer; you sense it's a favourite story. Does he ride now every day? "I love riding, but I live in LA and I'd have to drive - so it's more like a special occasion when I do."

Seabiscuit is the story of an underdog, which is another reason Maguire likes it. As his director mentioned, he had a tough and lonely childhood, without much money. In 1993, his father, Vincent, was convicted of robbing a bank in his home town of Reseda, California. He's been in famous brawls alongside old pal Leo DiCaprio when his posse were on the razzle in LA and New York (no doubt those days are long behind him in his new sober mode). He's not quite the squeaky-clean boy of his popular image.

The curious thing is that Spider-Man has not transformed him at all, and that his basic ambiguity - is he cynical or kind, ugly or beautiful, boy or man, feminine or masculine? - remains gloriously intact.

As he stubs out his cigar and prepares to leave for his flight to Germany, I ask him one last question. Ang Lee said that he had an innocence - what is the nature of your innocence? He smiles at the question. "It's a Jekyll and Hyde thing," he says, as his minders come in to collect him.