The Herald Magazine cover story.

The last time I saw Daniel Radcliffe in the flesh, there was plenty of it on show. It was at one of his acclaimed performances for the stage play Equus in London's West End back in 2007. I was sitting "in the round", literally looking down on him as he played unstable stable boy Alan Strang. And there he was, the actor known to millions as boy wizard Harry Potter, stripping in front of an audience for a role in which, in a fit of religious and sexual fervour, he blinds six horses. Say what you want about Radcliffe, but for a lad who was set up for life before he'd even moved out of his parents' home, that took guts.

When we meet, in Claridge's hotel, London, Radcliffe is wearing jeans and a bright turquoise V-neck T-shirt snugly encasing his slender frame. Four years on from his stage turn, he's about to watch the curtain fall on a franchise that's overtaken James Bond as the most successful series in cinema history. After a decade of donning those little round spectacles, Radcliffe is readying himself to say goodbye to Harry. Following the release next weekend of Harry Potter And The Deathly Hallows: Part 2 – an event that comes just eight days before Radcliffe turns 22 – there will be no more premieres, no more press, no more Potter.

While the final episode sees Harry inexorably head for a showdown with the evil Lord Voldemort, Radcliffe's journey is much less certain, as the portents already suggest. The last shot he filmed with co-stars Rupert Grint and Emma Watson, who play Harry's friends Ron Weasley and Hermione Granger, was of all three jumping into a fire (a crash mat, in reality). Talk about taking a leap into the unknown. "I don't think we were struck by the deep symbolism of it at the time but I can certainly see how there is a parallel to be drawn there," Radcliffe muses. So what happened when they got the shot in the can? "We all just sat around crying for a couple of hours."

As you would expect, Radcliffe is in slight denial about it all. "What's interesting is that it's not just going to go away," he says. "Because the age range of fans is so huge, we'll always be coming back to the films. I don't think there's going to be any kind of dwindling of the number of people that love the films and love the books, certainly not from my point of view."

He's right, of course. The endless Christmas repeats, the DVD reissues, marathon Potter screenings – it will run and run. That time when he stood in the wings at a Red Hot Chili Peppers concert in Hyde Park, only to hear the whole crowd start shouting "There's only one Harry Potter" after he'd been spotted, probably won't be a one-off.

"It's very hard to see Daniel and not think of anyone but Harry," says Tom Felton, who plays Harry's young nemesis Draco Malfoy and shares a passion for cricket with Radcliffe. "Even I've called him Harry for a couple of years. It's odd. It's what you know him as. It doesn't make it any easier that he looks just like Harry." Compared to Felton – who is far different to his blond-haired character – this is certainly true. Today, Radcliffe may not be wearing Harry's glasses, but the mop of brown hair and shiny blue eyes are unmistakable. Like the character, with his lightning bolt birthmark, Radcliffe is branded for life.

The question is, how does he deal with it? Will it put a stranglehold on his career? "When people say, 'Are you worried about being typecast?' – well, I haven't been so far," he answers. "Equus, for example, was quite a leap from Harry Potter. But I think one of the challenges will be to get people to see me as an actor rather than just one character. And to a certain extent, some people will always see me as this character. But the minute you accept that, it frees you slightly. As long as the people that see me forever as Harry aren't casting directors, other actors and directors, I should be fine in getting other jobs. So far I've been all right."

Given the limited time afforded him between making the eight Potter films, Radcliffe has certainly played it smart. Equus aside, there have been well-received film roles in Australian family saga December Boys and alongside Carey Mulligan in TV drama My Boy Jack, in which he played the son of Rudyard Kipling. He appeared on Ricky Gervais's Extras, riotously indulging in a little self-ribbing as a lusty version of himself who flirts with anyone, including Diana Rigg. "He was probably what most newspapers would love me to be in reality," Radcliffe smiles. He further mocked himself on Judd Apatow's Funny Or Die website, claiming to be Harry in real life, spending his time chilling out and talking to women.

After ticking off another comedy milestone – voicing a character in The Simpsons – Radcliffe has spent this spring on Broadway (following his 2008 stint there in Equus) for a revival of How To Succeed In Business Without Really Trying, Frank Loesser's 1961 musical about corporate ladder-climbing. Taking on a role previously inhabited by Matthew Broderick, Radcliffe is window washer J Pierrepont Finch, who manages to ascend through the ranks in New York's World Wide Wicket Company. He sings. He somersaults. He even takes part in a Busby Berkeley-style number, where he's passed through the air.

While Radcliffe has had singing lessons for the past three years, dancing was new to him. "I'd never danced a step in my life before I started to take lessons," he says. "It's a hard thing." In the end, it took more than 20 months to get it right. "There is nothing that can't be achieved by a lot of hard work," he says, beaming. If the musical is not as controversial as Equus, it's a role where, quite literally, you can fall flat on your face. So far he hasn't. With the show nominated for nine Tony awards, the critics have looked kindly towards him, Entertainment Weekly calling his work "triumphant".

Radcliffe is not one to let such things go to his head. As far back as the first Potter instalment, 2001's Harry Potter And The Philosopher's Stone, he can remember telling people on set that if he ever got cocky, they should tell him. As child stars go, he's been a model pupil.

"I think I cope quite well with it because I don't think of it in those terms," he says. "As soon as you start to believe you're a star, that's the moment you start to screw up. But also the other thing about the word 'star' or 'celebrity' is that it's fleeting. There's a phrase in football – 'Form is temporary and class is permanent' – and that's what I aspire to. I want longevity rather than a quick-burning career."

If you're looking for a person to bad-mouth Radcliffe, you won't find one. Scottish director and actor Peter Mullan, never a man to pull punches, worked with Radcliffe on Deathly Hallows. "He's the sweetest, nicest multimillionaire I've ever met," he winks. "He's a total sweetheart – I was blown away by Daniel – and lovely in every sense of the word. Utterly genuine. Nothing is a put-on. I was impressed."

Indeed, given that his fortune is estimated at £48 million, you'd hardly know it. With not a gleaming sportscar in sight, Radcliffe's biggest purchase has been a flat near his parents' house in west London.

Neither spoilt nor cynical, the actor exhibits an unbridled enthusiasm, whether it's talking about old arcade games, nu-rave band Klaxons or Potter lore. "Far too many people my age seem to be young and jaded already," he says. "These aren't people who've had tough lives – they've had great lives and educations. And you just think, 'What have you got to be jaded about?' I know it's not cool to be enthusiastic about things, but I can't help it. I was never particularly good at anything at school. I got by. I was rubbish at sports. But I found something I'm good at and I enjoy and so few people find that. I haven't got anything to be unenthusiastic about."

Still, it's not been easy being Harry, especially when there are more rumours surrounding you than there are spells at Hogwarts. Some are charming – such as ordering beer brewed by monks to be drafted on to the Potter set (not true). Others are just plain silly – he hasn't recruited the SAS to walk his dogs. Then there are downright bizarre myths – like splashing his fortune on a nude sculpture of himself for his living room. And, of course, there have been the ugly ones. Back in late 2009, reports emerged that Radcliffe had been snapped on a mobile phone supposedly smoking a marijuana joint at a party thrown by a friend of his now ex-girlfriend, the actor Laura O'Toole (whom he met while she understudied on Equus). The allegation was vigorously denied, with a spokesman saying: "Daniel does smoke the occasional roll-up cigarette, but he was not doing anything more than this."

For a decade in the spotlight, one negative (and refuted) story is pretty good going, though he recently revealed he had given up alcohol after become "reliant" on it while socialising. "There were a few years when I was just so enamoured with the idea of living some sort of famous person's lifestyle that really isn't suited to me," he told GQ magazine. "As much as I'd like to be a person who goes to parties and has a couple of drinks and a nice time – that doesn't work for me."

He admits now, "I do have to watch myself when I go out." Not one for fancy nightspots – Radcliffe prefers gigs and "old man's pubs" – he keeps his head down.

"There have been people who have tried to exploit me," he says. "You get chancers out there who just want to make a quick buck, but as long as you tune into them and who they are … The best thing I've learned is, if you're going out, never go out alone – you leave yourself vulnerable. If you've got someone else there you trust, they can say, 'Be wary of that person.' I probably used to be too trusting of people."

While there are always hordes of female admirers at the Potter premieres – including, memorably, one with a banner proclaiming "Mrs Radcliffe is here" – normal life is possible, he says. "I'm 5ft 5in, pale and skinny. There are not too many people that look twice, to be honest. People do stop you and talk to you in the street, but generally it's fine." There have been girlfriends – though nobody from the set of Potter (certainly not Bonnie Wright or Katie Leung, the actors who played the two characters Harry has flirtations with).

He has, of course, been well shielded by an inner circle – primarily comprising of his parents, his long-standing publicist and the film's producers. Raised in Fulham, it helps that his folks already had some understanding of the industry (his mother, Marcie, is a casting agent, while his father, Alan, is a former literary agent who gave up his job to act as his son's chaperone when he won the Potter lottery). So the story goes, Radcliffe was 10 when he was first given the chance to sign on for all seven book-to-film adaptations, all to be shot in Los Angeles. Unknown to Radcliffe, his parents – horrified at the idea of losing their only child to Hollywood – turned it down.

By this point, Radcliffe had already acted professionally. His early years at Sussex House, an independent school for boys in Chelsea, had been miserable. "When I was at school, I wasn't particularly good," he says. "I found it very hard to concentrate. I would end up talking to other people and not really listening to the teacher." Hardly the worst crime ever, but, in a bid to improve his confidence, his mother put him forward for the role of the young David Copperfield in a 1999 BBC adaptation of the Dickens classic. Winning the part, Radcliffe then made his film debut as the son of Geoffrey Rush's informant in the steamy adaptation of John Le Carre's The Tailor Of Panama.

It was during the shoot that he found out he'd won the role of Potter. It came after a chance encounter with producer David Heyman at a West End show meant he'd got a second bite at the cherry (his parents were by now more open to the idea, with the production moved to the womb-like Leavesden Studios near Watford). At the time, John Boorman, director of The Tailor Of Panama, was apparently heard to remark, "Oh well, there goes his childhood." Yet Potter has clearly been the making of Radcliffe – and not only financially.

"On-set, I had one-to-one tuition which forced me to pay a lot of attention, and learn a lot more," he says.

After taking his GCSE exams (during the making of the fourth outing, Harry Potter And The Goblet Of Fire), Radcliffe gradually drifted away from formal education. Would he ever consider applying for a place at university (as Emma Watson did)?

"The option is always open," he says. "I could go at any time. But I prefer to think that by reading a huge amount and watching the Discovery Channel, I will broaden my knowledge. I watch University Challenge every week, and I normally score between 15 and 20 – which is more than some of the contestants get. When that stops happening, I'll consider a university career, but at the moment I'm fine."

An avid reader, Radcliffe talks passionately about Russian author Mikhail Bulgakov, who wrote The Master And Margarita. "For my 21st birthday, I went to Russia and visited his house, which was very, very exciting." Radcliffe is also a fledgling art collector, owning works by New York-based artist Jim Hodges. And then there's his love of creative writing. He secretly published four poems under the pen name Jacob Gershon in Rubbish magazine in 2009. Some covered typically teenage topics such as Pete Doherty and Pop Idol, but one, Away Days, took a wry look at infidelity from the view of a businessman sipping champagne and toasting his own secret trysts with prostitutes.

In the past, Radcliffe has said people tend to think of him as a Peter Pan figure – undoubtedly a hangover from being so associated with a fictional schoolboy. But he is already working towards changing that. His first post-Potter film, due next year, will be Victorian horror The Woman In Black, an adaptation of the Susan Hill novel. "I'm playing a father and a widower – two things I don't have direct experience of," he notes. "Although I absolutely love kids. I think they're amazing and I can't wait to have some." He breaks for a second, aware his mouth is running away with him. Given the darkness of Deathly Hallows, it seems Radcliffe has already prepared his fans for this inevitable departure into more adult fare. Chances are, given his fragile build, he won't be playing the action hero again.

"The thing that people underrate about being an actor in a franchise like this is that you get to do things other actors never do," he says brightly. "For example, in the sixth film, I burst out of the surface of the water surrounded by a ring of fire. I could act for another 100 years and never get to do that again."

He looks sad for a second. "I will miss that." And after 10 years as the world's most loved wizard, we're going to miss him.

Harry Potter And The Deathly Hallows: Part 2 (12A) opens on July 15.