`Hit harder, George. Is that the best you can do?'

Zaire, 30 October 1974. For Ali and Foreman, their Day of Destiny. For Leon Gast, a chance to make the `African Woodstock'. Twenty-three years and 300,000 feet of film later, it was to win him an Oscar for best documentary.

It was billed as the Rumble in the Jungle. In Zaire, October 1974, Muhammad Ali challenged the invincible George Foreman for the heavyweight crown. It became known simply as "The Fight". And, for both men, that epic drama on the banks of the former Congo became a strange passage into their own hearts of darkness.

Such moments of personal revelation in the arena are the very stuff of sport. The reason the great compete. The essential motive for the rest of us to watch.

Leon Gast's stunning new film, When We Were Kings, captures that moment in time, in the context of its time, with a power and poetic punch rarely seen in sports documentary. And in March, Ali and Foreman were reunited on stage when Gast collected the Oscar for Best Documentary Feature and received the ovation of the night.

When We Were Kings took two months to shoot and 23 years to complete. "Originally, the film was conceived as an Afro-American Woodstock," says Gast, a 60-year-old New Yorker whose initial interest was in the three-day music festival preceding the fight.

On the bill were many heavyweights of the Seventies black music scene, including BB King, James Brown and the Spinners, as well as numerous African acts. "But as interesting as that might have been, it didn't compare to a film centring on the incomparable Muhammad Ali," Gast explains.

"But everything that could possibly go wrong has gone wrong. Maybe I crossed a witch-doctor while I was over there and he put some kind of a hex on me," he laughs.

The post-production budget that was to come from the festival's gate- receipts simply vanished when President Mobutu declared it a free concert. And although the dictator had put up the $10m purse to bring the event (and its attendant publicity) to Zaire, few of his impoverished subjects could afford tickets.

Then came a mixed blessing. The fight was postponed for six weeks when Foreman's eye was cut badly in sparring. And while the boxers, promoters and world's press fretted and sweated in the heart of Africa, Gast kept his cameras rolling, amassing 300,000 feet of film but returning to the States flat broke.

Next, the Liberian government, which was backing the film, was overthrown and the director was left to spend the next 15 years trying to re-finance his labour of love. In 1989, Gast joined forces with his former attorney, David Sonenberg, a music business manager who came on board as executive producer, and the pair set out to edit eight different versions of the film.

Having shifted the focus, Gast and Sonenberg tracked down additional fight footage and archival clips to compose what the director now calls his "love poem to Muhammad Ali". But something was still missing. In 1995, Hollywood director Taylor Hackford completed the picture. "I really think it's one of the seminal athletic events of this century - because it had theatre," explains Hackford. "It was right in the Seventies and right at the peak of the black power movement. But you want voices that can explain that historical context."

Hackford shot and intercut new interview footage with writers Norman Mailer and George Plimpton (who had both covered the fight in 1974), film- maker Spike Lee and Ali biographer Thomas Hauser. Their narrative and passionate memories provide an uplifting Greek chorus to Gast's visual drama.

Reviewers in the States have commented on how Mailer and Plimpton still enthuse about the Rumble in the Jungle as if it had happened only last night. Yet, in the film, Spike Lee saliently notes the collective amnesia on the part of young black Americans, who simply know nothing about men like Ali and Martin Luther King.

Although it is every generation's penance to sit through past tales of derring-do, we are spared the usual pitfall of athletes looking back. The commentators set the scene. Ali speaks only from the height of his powers and the editing evokes a past drama that is still present in the fight footage. The memory of one of sport's greatest hours is not just preserved for posterity, but brought to life again.

Sonenberg echoes Lee's point: "Many of my young rap artists had no idea who Ali was." So, to connect with the younger generation, Ali is recognised as "The Original Rapper":

"I have wrestled with a alligator,

I have tussled with a whale,

I have handcuffed lightning,

Thrown thunder in jail.

Only last week I hospitalised a brick,

I'm so mean, I make medicine sick."

In a strange twist, what was to have been a "black Woodstock" ends up prefiguring the future of Afro-American music.

Such unknown forces can indeed come out of Africa. Plimpton recalls an African witch-doctor whose premonition of the fight intriguingly set the supernatural tone for George Foreman's future destiny.

The seedy history of boxing promotion is littered with such "Days of Destiny", but 30 October 1974 transcended all the cliches. Foreman, the unbeaten, seemingly unbeatable champion, was, in Hauser's words, "this hostile ominous presence" who seemed to defy the laws of human physics. He said little, but spoke forcefully when he did. He kept his hands, like weapons, encased in his pockets.

Ali, at 32, had lost three years of his career after refusing to join the US army and was given no chance of outdancing his formidable opponent. Indeed, fears for his life were very real. Foreman's cornerman, Archie Moore, admitted that he prayed that Ali would not die in the ring. And a plane was kept ready at Kinshasa airport to fly him to hospital in Madrid.

But this epic event was also a celebratory return to the "dark continent", the homecoming of two Afro-Americans in a contest to find the King of Africa. "Ali was a king amongst kings - from Mobutu, the resident King of Zaire, to James Brown, the King of Soul, to Don King," explains Sonenberg. "But Ali, he was on a whole different level... Ali was King of the World."

Certainly, he won the hearts of all Africans. He praised their bilingualism: "Ain't that something? We in America are the savages." He used the extended build-up to become the people's choice, masterfully manipulating the press, loudly proclaiming himself as Champion of the Oppressed. Outside the ring, he had earned this title with his unique ability to fuse politics and sport.

Unlike both Don King and Foreman, who evade such issues in the film, Ali had donated thousands of dollars to philanthropic causes. And he had famously refused to fight the white man's battle. There was, as ever, rhyme to his reason:

"On the war in Vietnam, I sing this song,

I ain't got no quarrel with the Viet Cong."

But the heavyweight crown would be forged in that contest by the Congo, under an overcast sky that threatened an imminent tropical downpour. Norman Mailer is cast as a modern Marlow, leading us into the heart of both men's darkness that night.

We watch as Ali prepares his body for Foreman's thunderous blows. We watch him steel his will, rapping jabs at the pretender's psyche:

"He's the bull, I'm the matador. He's scaaared to death."

The great psyche-out begins. Ali's trick was to channel his fear into others and you can almost hear it leaving as he mocks the pervasive awe that Foreman inspires: "Scared a what, scared a what?"

Ali studiously avoids the fearsome sight of his opponent's battered punchbag. Ali, the myth-maker, chides Foreman for fighting "in my country". And everywhere he goes, he leads the crowds in the native mantra of "Ali boma ye, Ali boma ye" (or "Ali kill him, Ali kill him").

In his book, The Fight, Mailer relates the final doubts that Ali poured into Foreman's ear as the pair put the stare on each other just before the bout: "You have heard of me since you were young. You've been following me since you were a little boy. Now, prepare to meet your master!"

And as that hour begins to unfold, at the end of Round 1, it is the crowd's mantra we hear, but it is Ali's private thoughts we try to read on the most photographed face on earth as he struggles to overcome the horror of "this huge black force" he is faced with. And as the intensity of Ali's stare illuminates the screen, Mailer's magnificent musing on what goes on in a great athlete's soul at such a moment does justice to one of the most compelling moments in the history of sport.

Even while commentating on the fight, Britain's own Harry Carpenter pondered the possibility that it just might be the greatest boxing match ever seen. You get the same sort of feeling watching When We Were Kings.

Yet in Gast's version, it's not an entirely fair fight. The director fully acknowledges his bias towards Ali, leaving the character of the other man in the ring an unexplored enigma. Like a snake who sheds his skin in the jungle, Foreman underwent a metamorphosis after Zaire. Leaving behind the sullen, mean persona, he re-emerged years later, first as a preacher, then incredibly, in 1994, as the oldest man ever to win a heavyweight title.

But Foreman acknowledges his past: "I wasn't putting on an act. I was a bad man. And I wanted not only to win but to hit those guys and hurt them." And his feelings on Ali? "I hated him, I wanted to kill him. But this man was more than your ordinary boxer. He was the greatest. Just the association of his name with mine pretty much made me outside the ring."

None can compete with Ali's charisma and sheer courage. It was part of his genius to reinvent the sport itself, even as he rewrote its history. He shocked the world with his rope-a-dope tactics in Zaire: instead of dancing, circling his opponent, avoiding that right hand, Ali went on the ropes, where the full weight of Foreman's rage rained down on him. Leaning way back on the rigging, Ali invited disaster, taunting his foe: "Hit harder, George. Is that the best you can do? You disappoint me, George!"

In this question of sport, most of us know what happened next and to report it here would spoil the plot for any young viewers lucky enough to be seeing this thriller for the very first time. For their elders, it is fascinating to ponder the fates of the players since The Fight: Foreman has since transmogrified into genial George, the burger-munching grandfather of the heavyweight division. He is now one of America's most popular sportsmen. Leon Gast thanked the fighter in his Oscar speech "for what he was then and for the man he is today".

The silent warrior of the Seventies is now a very vocal public figure. He does the chat-show circuit, advertises hamburgers, and in April picked up $4m for his WBU title defence against Lou Savarese.

And Ali, who spent his twenties telling the world he was the greatest, and his thirties proving it, now seems destined to spend his old age being told that, yes, he actually was. The Louisville Lip is now silenced by Parkinson's syndrome, but, with typical bravery, he refuses to hide himself from his adoring public.

"Everybody else sees a man that is suffering from a debilitating disease," says Leon Gast, "but I know he's happy, that he's doing exactly what he wanted to do - and that is to go out and touch the people" n

`When We Were Kings' opens on 16 May

This is an edited version of a piece that first appeared in `The Title', Ireland's sports newspaper