Luciano Pavarotti: You know it's opera when the fat man sings

All opera requires a certain suspension of disbelief. But the audience at the Royal Opera House this Friday will need to suspend theirs absolutely. For in this performance of Tosca, the heroic revolutionary love interest, Cavaradossi, will be played by Luciano Pavarotti, 67 next birthday and so overweight that last time he performed the role here, in 1992, he spent much of the production leaning on props. Since then, he's had a hip and knee replacement and shed 50lb, but he still cuts a considerable figure. "Because of my size, people see me once and don't forget me," he once said.

Opera houses still adore him. Tickets for his four performances sold out immediately, and you can bet that most of the audience – from those who've paid £175 to sit in the stalls to those standing in the slips for a fiver – are there for Pavarotti not Puccini. The man is larger than life in all senses: immensely wealthy, hugely popular and, most important of all, prodigiously talented, even if his voice is no longer the vibrant, lyrical, honeyed instrument it once was. Albert Canto, the music critic for Il Giorno described it as "kissed by God and hailed by man" before berating him for singing "less and worse" and dabbling in popular concerts at the expense of opera.

It's a charge often levelled at him and one he must rise above this week. His appearance will be an important occasion for other reasons. "Singing at Covent Garden is one of the most special experiences for me – a big, big part of my life," he says. "It is always beautiful to see the same faces the moment you walk backstage". These will be his first appearances in the refurbished house and possibly his last. In 1996, he said his "goal was to sing until 2001, to complete 40 years in the profession"; he shows no signs of slowing down.

Next month he's singing in Montreal and Dallas, then back to Italy to record, followed by dates across the US and Canada, another run of Toscas at the Metropolitan in New York in May, plus concerts in Manchester, Marseilles, Lille, Birmingham and Nice. Unlike most singers, he will not commit to anything more than a year ahead. But nor will he say he's giving up. "If I feel good, if the audience like me – I'll keep going," he says. "At the end of these Toscas I'll decide what I want to do. I take things day by day. Every tenor ends up spending three years going round the world making farewell concerts; I suppose I'll do the same."

With annual earnings of an estimated $35m (£24m), he can do as he pleases. He has emerged from an expensive divorce from his wife, Adua Veroni, whom he married in 1961 after an eight-year engagement, and with whom he has three daughters, Lorenza, Cristina and Giuliana. He left her for Nicoletta Mantovani, a PhD from Bologna, whom he met when she came to temp one vacation at the Equestrian Centre (after music, horses are his passion) he owns in his birthplace, Modena, and who at 32, is younger than his youngest child.

Last autumn, the charmed life seemed to desert him. He appeared in court in Italy, charged with tax evasion to the tune of 40bn lire (£13.3m) and filing false tax returns between 1989 and 1995. He pleaded not guilty – "A singer expresses himself in the world. I do not feel guilty, and if a law says the contrary, I want everyone to know I was acting in completely good faith," he told the court – and was acquitted.

He divides his time between homes in Pesaro, a Central Park apartment in Manhattan, and two flats in Monte Carlo. But his origins were far from wealthy. His father, Fernando, was a baker and keen amateur singer, and his mother worked in the Toscana cigar factory. In his youth, Pavarotti sang in a local opera chorus, the Corale Rossini, with which he travelled to Wales in 1954 to take part in the Llangollen international singing competition. It won first prize, and as a result the teenage Pavarotti caught the attention of a local professional tenor, Arrigo Pola, who took him on as a pupil even though he could not afford to pay for his lessons. He was a diligent student (it is a myth that he cannot read music). "I am not a natural singer," he told BBC Music Magazine in 1993. "I must study because singing in the way you sing in the shower is not enough. You have to do something with great force under control and it is very difficult."

Uncertain that he would be able to sustain a career in music, he also trained as a teacher, before moving into insurance sales. He excelled, but was forced to quit because, he told an interviewer from Cigar Aficionado magazine, "all that speaking was damaging my voice. Talking can be harder on the voice than singing." He's not so protective of his vocal cords, however, that he doesn't indulge in mild cigars.

At 25, he won another singing competition, the Achille Peri; the prize was a professional engagement, singing Rodolfo in La Bohème in Reggio Emilia, an experience that convinced him that despite its insecurities, a professional career on the opera stage was what he truly wanted. There followed engagements in Belgrade, Amsterdam, Barcelona and, importantly, London in 1963 and Glyndebourne in 1964, where he met the legendarily statuesque soprano Joan Sutherland, who was on the look out for tenors taller than she was. Hard to imagine now, but Pavarotti was once a keen sportsman and cut a muscular figure. She was booked for four performances of Lucia di Lammermoor in Florida, and requested Pavarotti be cast opposite her – his US debut. Their partnership was a triumph, as was their subsequent tour of Australia.

According to the writer Norman Lebrecht, in his book When the Music Stops, "His projection was under-developed. It was Sutherland who, standing in front of him and placing his hands on her stomach as she sang, taught him to use his diaphragm. 'Every time I'd turn around, there he'd be with his hands on my wife's tummy trying to figure out how she supported her voice, how she breathed,' said Sutherland's husband, the conductor Richard Bonynge."

Pavarotti is grateful to them to this day. But Sutherland is only one of many figures who have shaped Pavarotti's career. Herbert Breslin, first his publicist and then his agent, was arguably the first to exploit his crossover appeal. "Luciano has something to offer and he is anxious to offer it to as many people and in as many different places as possible," he has said.

Why restrict a career to opera houses seating 2,000 or 3,000, when you could be performing to hundreds of thousands in stadiums and parks? The man responsible for making him a household name was Tibor Rudas, the impresario behind "The Three Tenors", the concert staged to coincide with the 1990 World Cup that turned Puccini's "Nessun Dorma" into a football anthem. The TV broadcast drew a worldwide audience of 300 million; the CD sold six million copies, making it the bestselling classical album of all time.

Pavarotti has never shied away from commercialism. His tastes are eclectic, or indiscriminate, depending on how you look at it. He's also performed, for his war charity Pavarotti and Friends, with Anastacia, Jon Bon Jovi, Eric Clapton, Celine Dion, Elton John, Tom Jones, George Michael, Lionel Richie, the Spice Girls and Barry White. There is vanity and affectation in the wielding of the white handkerchief, the heavily blackened brows – but also great enthusiasm. Opera remains his first love, his raison d'être. He scorns the idea that he has sold out. Rather, he has made it his mission to make an art form he loves loved by others.