At 23, the highest-rated player in the history of chess is also the face of the G-Star Raw label, or as they put it, its "global brand ambassador". Somewhere along the line the marketing department must have had a light-bulb moment and gone: "Chess and denim! Made for each other." Suddenly, chess has become super cool. Last year, Carlsen was voted one of the world's 25 sexiest men by Cosmopolitan magazine.

Just now the beetle-browed prodigy is a few feet away behind a screen, being interviewed by another journalist. I am next and, I admit, apprehensive. I have read he is easily bored (there is a theory that Carlsen sometimes deliberately loses the first few games in a tournament in order to make life more interesting); probably shy (in an interview for The New Yorker he barely made eye contact with the journalist) and possibly arrogant. It turns out he isn't arrogant - just blessed with self-belief, which is different. Unusually for the anorak world of chess, Carlsen is a celebrity. He could easily have had his head turned by the attention, but hasn't.

He is applauded for show pony tricks, checkmating Microsoft's Bill Gates in nine moves on prime-time TV for example, or playing blindfold chess against 10 players at once in a shopping mall.

By the age of six he had remembered the flags and capital cities of every country in the world; at seven he could identify any brand of car, singing out their names when they were but distant specks on the highways of his native Norway. I add "query Asperger's" to my list of questions.

It doesn't start well. Carlsen is slouched in a chair preoccupied with his smartphone. He shakes my proffered hand without looking at me and returns to his screen. There is a chair beside him but it has a plate of canapés on it, as does the one next to that. A large chess board completes the cordon sanitaire around him. I go to move the first lot of canapés and he looks faintly alarmed, or annoyed, it's not clear which. It's just so we can have my recorder close to both of us, I explain soothingly.

He's been watching the Australian Open tennis on his phone, he says, and just saw Stanislas Wawrinka beat Novak Djokovic. He likes all sport and plays it well - he could have been useful on the soccer field if the chessboard hadn't won him over. He entered his first international chess tournament at the age of nine and these days is on the road 160 days of the year. In his downtime, when he's not analysing chess games or working on moves, he plays online poker or watches sport. Is it lonely sometimes? "Sure, but I'm used to it," he says. "I'm comfortable with my own company."

Has he made friends on the circuit? "I have some, but they are not my main opponents," he says. "It's too hard to be friendly with them, they are more like colleagues, you could say."

Does it puzzle him, then, that top tennis players such as Djokovic and Andy Murray are close friends with each other? "I don't think they are," says Carlsen. "I don't think they can be; they probably enjoy each other's company but it's just hard to ... for any serious competitor to be close friends with the people you are trying to beat every day."

He may be no. 1 - and there are those like legendary former world champion Garry Kasparov who claim that chess has entered "the Carlsen era" in which he will continue to dominate - but the margins at the top are very small and there are always pretenders to the throne. According to Simen Agdestein, Norwegian grandmaster and Carlsen's former coach, his most serious rival at the moment is the Armenian player Levon Aronian, who could well be the one to challenge him for the championship this northern autumn. Agdestein is the author of Wonderboy, a biography of Carlsen. I ask what gives his former pupil the edge over rivals? "Other players have too much respect for him," he says. "And Magnus is the master of taking advantage of that, he is an expert in the psychological game." Carlsen also, famously, trusts his intuition. He may take 30 minutes to make a move but, as he told an interviewer in the run up to the world championship last year, "I usually know what I'm going to do after 10 seconds; the rest is double checking. Often I cannot explain a certain move, only I know that it feels right, and it seems that my intuition is right more often than not."

It is this almost magical thinking that led to Carlsen being dubbed "the Mozart of chess". The now overused phrase was originally coined by another grandmaster, Lubomir Kavalek, in the Washington Post in 2004 after Carlsen's match against Sipke Ernst, 12 years his senior. "It was a fresh, beautiful, imaginative masterpiece, created with lightness and ease," explains Kavalek later. "Something Mozart might have composed in music at the age of six. Magnus was 13."

Carlsen has operated in an adult world from a young age: how did he cope? He shrugs: "It was not a problem, I could be a normal kid at home; at chess I played like an adult." He was indeed precociously relaxed, sometimes getting up and walking around the room during a match, which raised eyebrows. Was he conscious of breaching etiquette? "I may have broken some rules when I was young, but I didn't understand and people didn't tell me. Anyway, I think walking around when it's not your move is okay, it's healthy for your brain not to sit all the time."

He works out, sleeps in until a couple of hours before a match and is strict about diet - no carbs before playing - taking a Norwegian cook with him to the world championship in southern India to avoid the risk of an upset stomach. In his hotel room he analyses openings and moves, sometimes with the help of a computer, though unlike most players he doesn't like to compete against them, preferring human opponents. His father regularly accompanies him to tournaments: "We eat dinner together, maybe play a bit of bowls." His father seems like a lovely man, I tell Carlsen who smiles for the first time. "I've heard that from many people, but I still don't get it," he says mischievously, a slow grin stealing across his face like a ray of light.

Henrik Carlsen taught Magnus to play chess, ferried him to coaching and competitions for years and eventually gave up his job as an oil executive to devote himself to his son's career.

"I think he enjoyed the chess so much more that he preferred to do that instead," says Carlsen. "At home he takes care of meals, works around the house. My mother still works full-time."

Carlsen grew up with his three sisters in a comfortable suburb of Oslo; their parents, both engineers, encouraged involvement in music, art and sport - at one stage taking them out of school for a year to travel around Europe. At mealtimes, Carlsen would sit at a separate table with a chessboard. So that was

allowed? "Yes, I get on well with my family, but that doesn't mean I had any desire to talk during meals. I'd rather be reading a chess book or moving some pieces around, that was normal for me."

He raises dark brown eyes: "But now I enjoy sitting and talking with my family. I think I've evolved a bit in that sense."

I ring Henrik Carlsen at home in Oslo to ask about the separate tables. "It wasn't so strange," he says. "We had always allowed the children to read books at meal times; Magnus just needed the extra space." There is only 18 months between Magnus and his older sister, Henrik tells me, so they did a lot of things together. "He was not a quicker learner than she, but he pursued things for longer. She would move onto something else and four months later Magnus would still be building Lego cities. It was the same with everything: whatever he did - football, reading - he had the most amazing concentration."

Did that concern him? "Of course we were constantly worried in the way that all parents are about children," he says. "But we did make sure he spent time with friends and doing sport. We didn't impose too much discipline; it's the Norwegian way to let children find for themselves what they want to do."

When Magnus was ready to start school, says Henrik, the head teacher suggested he go straight into second grade. "But we said no, he was small for his age and a bit shy." Yet he played chess with adults from the age of nine.

Prodigies can often have a hard time socialising. "We didn't think that was a problem," says Henrik, a keen amateur player himself. "Chess people are intelligent and interesting, not superficial." Did they realise they had a genius on their hands? "It depends how you define genius," he says. "But I guess you can say his chess performance is at genius level. Did anyone suggest he might have Asperger's? Henrik seems unsurprised by the question but says, "I know several kids with Asperger's and Magnus is not like them. He stores information and uses logic, and he can memorise chess positions because each one is like a story."

Carlsen recently moved out of the family home into a flat in the centre of Oslo: it gives him a little more freedom, he tells me. But when I ask what makes him happiest he has no difficulty answering: "Probably being with my family. Whenever I spend a longer period of time with them, on vacation in our mountain cabin or whatever, it adds to the quality of my life." When I relay this exchange to Henrik, there is a brief silence on the end of the phone.

"Well, thank you for telling me that," he says. "You've made a friend for life."

Earlier that day I watched Carlsen being photographed, standing impassive while stylists twitched at clothing and powdered his nose. G-Star's Shubhankar Ray told me: "When we first saw Magnus on TV in a chess tournament we thought he looked more like a boxer than a chess player. His aggressive style of play matched the DNA of G-Star Raw and we knew he would look good in our tough street clothing."

Does Carlsen enjoy the accoutrements of success - around £1 million ($1.8 million) a year in endorsements, nice gear, posing around looking sultry with beautiful women like Liv Tyler and Lily Cole? "I enjoy that people appreciate the game of chess," he says.

He is involved with an organisation called First Move Chess in the US. "The idea is to get chess into the normal school curriculum," he says. He was never much taken with school himself and would like to see chess in Norwegian classrooms. "It's amazing how much fun the American kids have - they're learning maths, how to think, but they don't consider it school work."

Carlsen has always said he will continue to play chess as long as it's fun. Can he imagine what his life would be like without it? "I don't know exactly what I'd do, but I think I'll eventually figure it out. Maybe at some point I can be what my father is now - a family man who doesn't have too many worries and just enjoys life." There could be rather a big gap between now and then. "Yes, I might find some other interests. I am working on a chess app - that is part of my brand. Definitely my brand will live on in a sense."

Does he imagine being married, having children? "Definitely yes. Just a few years ago I didn't think about those things at all. Now I do." He doesn't have a girlfriend, despite many female fans. Presumably there are not many women on the chess circuit, and none at the top? "Not too many, no. I think it has mainly to do with tradition. I don't think there are genetic reasons why women shouldn't be among the best."

He pauses then adds: "Just perhaps one thing favours the man: you have to be merciless. I know some of even the strongest female players of all time have said they sometimes feel sorry for their opponent." He shakes his head: "That makes it hard to reach the very top."

Lead-in photograph by Pal Hansen/Contour by Getty Images. 

MAGNUS CARLSEN IN BRIEF

• 1990 Born in Tønsberg, Norway, on November 30.

• 1999 Plays first international tournament at the age of nine.

• 2004 Becomes a chess grandmaster at the age of 13.

• 2008 World ranking rises to No. 6.

• 2009 Hires former world champion Garry Kasparov as his coach.

• 2010 Hits No. 1 spot aged 19, the youngest in history.

• 2011 Drops to No. 2 in the world. Invites 16-year-old grandmaster Wesley So to train with him.

• 2012 Wins Grand Slam Masters Final and most other major events.

• 2013 In February, reaches the highest Elo rating to date of 2872.

In November, beats Viswanathan Anand to become world champion.

• 2014 Wins in Zurich, the first serious tournament since capturing the world title.

Eight qualifying players will compete in the Candidates Tournament in Russia in March.

The winner will challenge Carlsen for the world championship in November.

MINI MASTER

By day, Anton Smirnov is an unassuming schoolkid at Sydney's Killara High School. At night he's a slayer of international grandmasters, the best chess player in the world born since 2001.

Barely 150cm tall and just out of primary school, Anton has no trouble beating players twice his size and four times his age. At the Moscow Open three years ago, he was referred to simply as "the little kid from Australia". These days, at 13 years old, he rarely plays anyone under the age of 18.

Just last month, Anton won the Australian under-18s junior title, and came within a whisker of claiming the Australian Chess Championship. On the way through he beat 55-year-old Australian chess legend, and the country's second grandmaster, Darryl Johansen. "He's learnt to defend very well and you can use the analogy from AFL football, the best defensive sides often win grand finals," Johansen says.

"In chess, often it's best to start young because life gets a lot more complicated when you get to your teens."

Anton was introduced to the game at four by his Russian father Vladimir, a chess master himself. He's grown up in a Russian-speaking household, and also has a gift for mathematics.

"Several years ago, when I was three-and-a-half [years old], I could multiply up to the thousands in my head," Anton says. "Like a random number, say 2364 squared. My dad told me the steps; I just had to remember the numbers and add them. I think it helps memory. You have to calculate moves [in chess]."

Anton's goal is to become a grandmaster. Australia has produced just four, compared with more than 500 by the ex-Soviet Union. Our greatest player and first grandmaster, Ian Rogers, believes Anton has the talent to do so.

At last count, Anton had 13 stamps in his passport. He loves winning, and is determined to keep improving. "It's not that impressive winning a tournament where everyone else is below you," Anton says. "If you win a tournament, probably it's not such a good tournament for you to play in."

- Interview by James Buckley

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