When supercool Ice Borg's long tennis reign ended, his self-discipline melted and his life fell apart. Now the veteran Swede is back in control and taking his last bow

So this is it, the final farewell. At 44 years of age, and after 27 years as a professional, Bjorn Borg, the supercool Swede, retires this week from tennis for good - apart, of course, from the occasional exhibition match or special event. He is bowing out at the ATP Seniors Tournament at the Royal Albert Hall, where he will most likely meet his greatest adversary, and temperamental polarity, John McEnroe.

It was against McEnroe in the 1980 Wimbledon final that he played what many observers believe to be the finest ever game of tennis. The match went to five sets after McEnroe won the legendary tie break in the fourth, 18-16. 'Whenever I looked at Borg,' McEnroe later admitted, 'I felt I was looking at a death mask.'

Perhaps more than any other sportsman, Borg exerted an inescapable psychological grip on opponents. When he walked out on a court his emotions seemed to retreat behind an unbreachable fortress of concentration. Somewhere beneath the headband, the blond mane, the wispy beard and rigid nose, was buried a tiny pair of blue eyes. And they gave nothing away.

From 1976 to 1981 Borg won 11 Grand Slam titles - five Wimbledons in a row and six French Opens - and 22 successive singles victories in the Davis Cup. Dubbed Ice Borg, he had a pulse rate of 35bpm. Ilie Nastase suggested he was from another planet. Some commentators wondered whether he was not in fact an android. Clive James compared him to a Volvo, wrongly declaring him 'very dull'. And everyone agreed he was utterly 'inscrutable'.

But Borg did betray signs of pressure; we just never saw them. He had a secret gesture he would make to his wife, Mariana Simionescu, who was sitting in the stands - a hand movement across his legs. It meant: leave the stadium. Now!

'By allowing myself to be used as a whipping-boy for his anger,' she would explain, 'I helped him stay cool.'

'It was an act,' Borg has said of his unruffled exterior, 'an act I came to perfect. But an act just the same.' With hindsight it's clear that the epic McEnroe match in 1980 marked the beginning of the end of the act. On 15 January 1981 at the Volvo Masters in New York, something strange and unprecedented happened. Borg argued with an umpire and had a point deducted. He was playing McEnroe. That summer he lost to McEnroe in the final at Wimbledon, a defeat he still thinks he should not have suffered, and, even more crushingly, in the US Open final. 'I was so disappointed,' he confessed. 'I thought it was the end of my life.'

He left the court before the awards ceremony ended and went straight to the airport in his tennis gear. In a sense, he also left behind tennis. It would be another two years before he officially retired, before his 27th birthday, but he never again found his will to win.

Borg has denied that McEnroe was his Nemesis. Rather, he says, he wanted to escape the regimentation, described by Simionescu as room service, practice, room service, practice, room service and no sex (it might affect his stamina).

And so he embarked on his second act: international playboy. He was already a tax-exile in Monaco. If Borg approached tennis with supreme discipline, he put no less effort into his new pursuits. 'You wake up and say, "What shall we do today?" he said of his new freedom.

One day in Stockholm, in 1984, his answer to that question turned out to be judging a wet-T-shirt competition. He voted for a 17-year-old nurse called Jannike Bjorling. He was sufficiently impressed to set up home with her. His marriage to Simionescu came to a speedy end. The new couple had a boy, Robin, but split up when Borg met an Italian pop singer and former porn star named Loredana Berte, variously described as six or 14 years Borg's senior. A custody battle for their son led Bjorling to accuse Borg of being a cocaine addict. He claimed she was promiscuous.

This was Borg's most challenging period. As he later observed: 'It wasn't until I stopped playing tennis that I realised that in real life problems exist.'

Despite receiving two astrological charts a year, he was unable to foresee the approaching crises. His fashion business ventures collapsed and he was personally sued by creditors for $1 million. He had his stomach pumped in a hospital emergency ward in 1989 after what many saw as a suicide bid, but which Borg has always claimed was a combination of bad fish and sleeping pills.

An attempted tennis comeback in 1991 ended in embarrassment. He played with a wooden racket, by then almost an antique, and was regularly beaten by the kind of players who would have frozen in his presence at his icy peak.

Meanwhile, Berte did not accord with the traditional Swedish view of female passivity. She was said to have scandalised the King of Sweden by exposing her red leather suspenders at a formal party. Of his second wife, he wrote in his autobiography: 'It was all sex, sex, sex.'

After Berte's own failed suicide attempt, the marriage came to an end in 1993. That same year Borg met his current girlfriend, a Texan called Kari Bernhardt, and the seniors circuit was launched. Borg found a way back: to tennis, success, and some much-needed order. As he said of his lost decade: 'I'm a Gemini and we're not that stable to begin with.'

Borg had started playing tennis at nine, when his father, according to Swedish folklore, won a racket in a table tennis tournament. At 12 he was suspended from playing tennis for a few months, owing to his poor court behaviour.

He left school at 14, already seen as a potential champion, to devote himself to the sport - and, following the well-established child-star syndrome, spent many years in his twenties and thirties attempting to reclaim his mislaid youth.

In running away from tennis he wanted to find the teenager he suppressed for tennis. The irony is that it was probably tennis that enabled him to relocate his identity. On the senior circuit, a nostalgic confection of camp competition, he relearned his act, but this time he hasn't had to suffer for it. The man who could make Ingmar Bergman look happy-go-lucky has even become close pals with McEnroe.

'He can be funny with friends,' says the American. 'With others he doesn't think conversation is necessary.'

It's somehow heartening to know that Borg can still freeze people out. It may be an act, you feel, but it's based on natural Scandinavian talent.

Now, having experienced his mid-life crisis in his twenties, he's about to retire, for the last time, in his forties. Life has moved at a rapid pace for the young boy from Södertälje. For most of us, though, it will be forever stuck on the Centre Court in 1980, as he plays another of those top-spin passing shots that came from nowhere and went straight into history.

Bjorn Borg

DoB: 6 June 1956, Södertälje

Playing career: Left school at 14; selected for Swedish Davis Cup team, aged 15. Wimbledon Junior Champion, aged 16. Wimbledon Champion 1976, 1977, 1978, 1979, 1980. French Open Champion six times between 1974 and 1981; 62 singles titles in all. First retired in 1983.

Borg on Borg: 'My greatest point is my persistence.'