When Muhammad Ali rumbled in the jungle with George Foreman exactly 40 years ago on Thursday, they were safely distant from the dying embers of a conflict that still engaged the more perilous commitment of 1.5 million of their compatriots in Vietnam. These champion pugilists, neither of whom fired a shot in defence of their flag, were sufficiently distracted by the lure of considerable riches to devote their full attention to the relative triviality of a fist fight, albeit one they would conspire to fashion as perhaps the most memorable in the history of their sport …

Vietnam had begun to recede from the popular consciousness in America in the early ‘70s. It was a reviled war, an embarrassment. Servicemen returning from their term of duty would land in San Diego and disappear into the hinterland rather than go home, finding refuge in drugs, alcohol or wretched anonymity. There were few homecomings, in fact, not many yellow ribbons tied around the old oak tree, the symbol of thanksgiving for sacrifice. This was the war America no longer wanted, and the young men who died latterly for its discredited cause in 1974 and ’75, when the final bell went, were in many cases abandoned as collateral damage. Back in Australia, I had just missed the draft for that misguided conflict and was well glad of it.

But in a period of receding tumult, there was Ali still, the objector of conscience, punching and talking again. He had reclaimed his boxing licence (after being banished in 1967), dismissed Jerry Quarry in three one-sided rounds in October 1970, in Atlanta, the only place that would sanction the fight, and went on to rebuild the career he had been willing to sacrifice on behalf of the Nation of Islam.

There was a considerable hunger to see Ali, inspired initially by the vocal support of the college students who listened to his anti-war message while he was in exile, then sustained when his media friends returned to the fold, aggrieved on his behalf as the legal process dragged slowly on. Once reinstated, Ali looked pretty good for someone who’d been away for three-and-a-half years.

Joe Frazier beat him in the Fight of the Century in 1971, but 13 wins of varying quality (including a low-key rematch victory over Frazier) and a split decision loss to Ken Norton followed over the next three years, and Ali, to the amazement of everyone but himself, was bigger box office than in his pomp.

His revival, illusory though it might have been, suited everyone: the boxing public, the TV stations, the promoters and the rest of the heavyweight division. The sport had been dull in his down time; it needed his noise and his style. He was slower, of course, throwing more but heavier punches from a flat-footed stance, with less dancing. It seemed not to matter, none the less, that, by the time he reached Zaire, he was 32 and visibly diminished.

Not a single respected critic spoke up for him. He was 40-1 with some bookmakers and nearly every expert feared for his safety against the monster that was Foreman. Yet intellectuals and artistes across the board – from Hunter S Thompson to Norman Mailer to George Plimpton to James Brown – mixed with boxing's regular cast of scoundrels. They came not so much to witness a legitimate world heavyweight title fight as to bathe in the glow of a legend who refused to leave the party, a hero who would surely provide them with a story, however sad.

In one of the most bizarre settings for any boxing match – with a thunderous storm advancing, in a stadium in Kinshasa once used as an execution chamber for dissidents – Ali made such an impact he earned the right to be regarded again as King of the World. It was a surreal episode from start to finish, stretched over a couple of months through circumstance (a cut to Foreman's eye in training), accompanied by a musical extravaganza, which was filmed brilliantly for posterity and no little profit.

Ali brought something special to every event, from walking into a room, to defying his government, to knocking out the awesome Foreman in the eighth round of their fight at 4am on October 30th, 1974, supposedly bolstering the regime of the troubled nation's despotic leader, Mobutu Sese Seko Kuku Ngbendu wa Za Banga, who ruled from 1965 until 1997. Ali's second coronation was completed in the home of his ancestors, a return to his roots, but it could be fairly argued that he played his part in extending the cruel governance of one of the poorest countries in the world. None of that concerned either Ali or Foreman – or the man who put the fight together, Don King. They were part of the fight game. A lot of bad things happened and are forgotten in the fight game.

We are all master of our own actions, of course; Ali gave up three-and-a-half years of his career in defence of that principle, and risked prison by standing up for a religion as menacing as it was righteous. Still, he chose to take $5m (a sum matched for Foreman) to fight in Mobutu’s Rumble in the Jungle, because it was Mobutu’s Rumble, really, not Ali’s. It was Ali who made it unique and he happily took the money that King scared up for them in London and Switzerland through Barclays Bank and the intervention of John Daly, a member of a well-known south London boxing family who would go on to become a Hollywood producer. Daly was the intermediary who pulled many of the interested parties together – and, as a prize, he got to commentate on the fight for Leon Gast’s celebrated film, When We Were Kings. Daly and the rest of us had to wait 22 years to hear and see his handiwork, however, because contractual disputes delayed release of the film – which won an Oscar. Its early screenings coincided with Ali lighting the flame for the 1996 Atlanta Olympics, his once feared right hand, palsied by Parkinson’s Disease, quivering in front of a television audience of billions. He was back in centre ring, where he felt most safe.

As for the fight itself, Ali risked destruction by using slackened ropes to lean eccentrically out of reach, back arched, rendering him intermittently safe from the oak-tree arms of the hitherto unbeaten Foreman, draining George’s strength and self-belief until he picked the right moment to launch his quicksilver raid on the crude ogre’s chin.

After soaking up Foreman’s best blows and misses, Ali came off the ropes to floor him with a final right hand that was just about perfect. The right that had decked Liston in their 1965 rematch, despite all suspicions, was probably of a similar force, except it was not so visible. There was no missing this blow. When Foreman wheeled and collapsed, his dazed head rising briefly from the canvas to see nothing but the ring lights and the jungle night, history had been rewritten. Ali told reporters he chose not to add another punch as Foreman fell, lest he spoil the symmetry of the descent. Maybe that was so.

The Cassius Clay I adored when shadow-boxing in his image as a 10-year-old was back. He'd just changed his name – and his shape. He didn't move like an angel anymore, but he had delivered one more time, hadn't he? Like he said he would. How could we ever have doubted him? Ali was the huckster who turned out to be real. He bullied you into believing in him. And the more he kept proving doubters wrong, the stronger was the conviction among the faithful that there would be no end to the miracles. For as long as he wanted to, he would keep winning. It was an illusion, naturally. We were all fools – including Ali. He thought he was invincible again. Soon he would be reminded of the consequences of his self-deception, not in defeat but in victory.

What was to follow in the last superhuman effort of his career – victory after 14 brutal rounds against Joe Frazier in the closing episode of their trilogy – was a prelude to a gruesome ending. Even as he neared the exit, there were other signs of spiritual degradation. He was philandering on a grand scale, oblivious to the hurt he might be causing those close to him.

He did not appear to care. It was as if he thought he was above normal judgment. The man with so much love in him was giving too much of it away to the wrong people. His epic saga began to unravel messily, at first flirting with self-destruction in Manila, when Vietnam, the war in which he refused to fight, was moving towards a conclusion every bit as ugly as his own disintegration.

The last round of the Vietnam struggle will be forever remembered in the image of retreat by over-loaded helicopters from the rooftop of the American Embassy in Saigon on April 29th, 1975, with locals begging for passage, knowing the fate that awaited them as enemy troops moved through the streets of the southern capital. There was no righteousness left in the fight now, no more punches to throw. Like Ali, America and South Vietnam no longer had a quarrel with the Viet Cong.

The final chapter of Ali’s nightmare, meanwhile, was 10 bruising pages from its conclusion.

This is a revised extract from Kevin Mitchell’s latest book, How To Think Like Muhammad Ali, published by Aurum Press, on Thursday – the 40th anniversary of the Rumble in the Jungle.

Guardian Service