These days the eyes of Muhammad Ali, once so sparkling and mischievous, are invariably hidden behind sunglasses.

The body, as he celebrates his 70th birthday, is frail, the gait uncertain, a walking frame or the arm of an aide often required.

Yet more than 30 years since Ali hung up his gloves after losing his last fight against Trevor Berbick at the age of 39 years and 328 days, following a career forged amid a golden generation of boxing heavyweights, he remains the greatest sportsman who ever lived.

Mention his name and the chances are it will conjure up a kaleidoscope of memories.

Great fights such as 'The Rumble in the Jungle' against George Foreman and the 'Thrilla in Manilla' against Joe Frazier, whose funeral Ali attended in November.

Moments of great courage, too, such as the lighting of the Olympic flame at the 1996 Olympics in Atlanta when Ali, ravaged by the effects of the Parkinsons disease he has endured for 28 years, gave the world's greatest sporting festival an iconic image.

You do not have to be middle aged to appreciate the breadth of Ali's achievements. You just have to take a passing interest in the history of sport and its ability to mould and shape the world around us.

Ali is not just a 70-year-old has-been. His career is a reminder of how far sport can take those determined to ride their natural gifts, in Ali's case hand and foot speed which saw him win the Olympic heavyweight gold medal in Rome in 1960 before turning professional.

In a boxing world which currently lacks credibility, with its plethora of title organisations and its myriad of weight divisions, it is difficult to convey the kudos the world heavyweight title bestowed back in Ali's day.

Suffice to say that he was, almost certainly, the most famous individual on the planet.

If his latter years had been kinder in health terms, no doubt he would stand up at his birthday party in his house in Paradise Valley, Arizona, with Lonnie, his childhood sweetheart and now fourth wife, and for old time's sake launch into one of those eloquent examples of the 'Louisville Lip.'

He'd enthral his friends with tales of Foreman and Frazier and Ernie Terell and Jerry Quarry. He might explain how he managed to fight on to win by a split decision after breaking his jaw against Ken Norton.

Almost certainly he would wax lyrical about the night he fought what has been deemed the perfect fight against Cleveland Williams, stopping his opponent in the third round.

He might even mention the time he felt 'Enery's 'Ammer, the left hook of British heavyweight Henry Cooper, in front of 45,000 British fight fans on a night mired in controversy when the laces of his gloves inexplicably came undone gaining him vital seconds to recover from a crashing knockdown.

He'd reminisce about the days when reporters recorded every syllable of his pre-fight patter.

"If you even dream of beating me you'd better wake up and apologise," he famously warned one opponent.

Instead, these days Ali lets the black-and-white television pictures or the early-morning closed-circuit cinema showings of him at his precocious best do the talking.

Some say Joe Louis was the best heavyweight boxer the world has ever seen and perhaps technically he does just eclipse the boy who was born Cassius Marcellus Clay on January 17, 1942.

But in terms of greatness there is no contest. Ali transcended sport. He proved greatness is not solely to do with what happens inside the ring or on the athletics track or on the football field.

When he told us how he "roped a dope" in Foreman, we chuckled at his humour.

We marvelled at his eloquence when discussing the world's problems with popes and presidents. We respected his objection to the Vietnam War which cost him three years of his career.

We were at first quizzical but then accepting of his conversion to Islam and his consequent change of name.But mostly we were bedazzled by the lightning hands and feet of the fastest heavyweight in history as he saw off the likes of Sonny Liston, Foreman and Frazier.

In all he held the heavyweight title three times, winning 22 world title fights and losing three, including his ill-advised brutal encounter with former sparring partner Larry Holmes when he was already in the midst of physical decline and sporting a bloated body and wandering mind.

Some would say that is nothing unique and that Evander Holyfield and Lennox Lewis have also held the world title three times.

That, however, would be to miss the unique energy and humility of Ali, a man whose boastful 'I'm the king of the world' catchphrases were always tinged with an endearing dash of self-mockery.

Only footballer Pele and golf's Tiger Woods, prior to his self-destruction, come near to emulating Ali's universal sporting appeal, men who when they play, hold the world in awe.

Some might say Carl Lewis, Jack Nicklaus, Don Bradman, Bjorn Borg and maybe even Babe Ruth, the greatest player in baseball history, deserve their place in that debate.

But, when all is duly considered, one man is way out in front. The man who "floated like a butterfly and stung like a bee".

It is no longer possible to know what truly goes on behind those sunglasses.

But the memories remain. And for that all sports lovers should raise a 70th birthday toast. Muhammad Ali, still the greatest.