Thirty years after his death, the remains of Ernesto 'Che' Guevara, whose hands had been cut off following his execution by his Bolivian army captors, were finally returned to Cuba, the homeland he adopted and helped remake in his image. His final resting place is a mausoleum in the suburbs of the city of Santa Clara, a site of almost religious significance to Cubans who lived though the revolution of 1959. Vallegrande, where his corpse was put on public display following his execution, remains much as it was, a forlorn place with little trace of his presence save for the hawkers of cheap Che memorabilia who wait for the tourist buses. On the wall of the town's public telephone office, someone has written, 'Che - alive as they never wanted you to be'.

In the tumultuous year that followed Guevara's death, that sentiment was echoed in the slogan 'Che lives!' which appeared on walls in Paris, Prague, Berkeley and Belfast. During the political unrest of 1968, it became a clarion call for what seemed like a spontaneous global insurrection and, for a brief moment, it seemed like the old order - capitalism, the Cold War, conservatism, militarism - might actually be replaced by something (though what exactly was never defined) younger and freer. That something was symbolised by the doomed romantic figure of Che Guevara, whose short life ended in a kind of martyrdom in the mountains of Bolivia, where the CIA openly admitted their role in his capture.

'In a way, 1968 began in 1967 with the murder of Che,' says the author and political journalist, Christopher Hitchens, who describes himself as 'a recovering Marxist, not ashamed, not unbowed, but thoughtful'. Like many who came of age politically in the late Sixties, Hitchens was in thrall to the personality cult that attended Che. 'His death meant a lot to me, and countless like me, at the time. He was a role model, albeit an impossible one for us bourgeois romantics insofar as he went and did what revolutionaries were meant to do - fought and died for his beliefs.'

Almost 40 years on, the wave of romantic revolutionary idealism Che helped ignite seems as unreal as Alice's wonderland, and the Communist ideology that inspired it dated and anachronistic. Che's defiant image may still hang in the offices of Andy Gilchrist, leader of the Fire Brigades' Union, and Bob Crow of the Rail, Maritime and Transport Union but, politically at least, it is a relic of a bygone era, as arcane in its way as as those old ornate union banners. Internationally, too, Guevara's ideological legacy is in tatters, his memory kept alive only by the few remaining leftist guerrilla movements such as the Zapatistas in Mexico, or the recently established People's Democratic Republic of the Congo, whose guerrilla leader Che trained back in the Sixties.

In Cuba, Guevara remains a quasi- saintly figure, as well as a symbol of what was, and what might have been, in Castro's now faltering state. Though it has survived decades of sanctions and attempts to assassinate its leader, the socialist republic of Cuba is now under threat from within: sex tourism and Castro's treatment of dissidents and gays have long since sullied the idea of equality that underpinned the revolution of 1959. And yet, the myth of Che endures.

That myth has long since floated free of Cuba and its revolution, becoming an amorphous entity that has little to do with Guevara's politics or the historical context that produced him. In 1967, the same year that Che died, the radical French activist Guy Debord wrote The Society of the Spectacle which, among other things, predicted our current obsession with celebrity and event. 'All that was once directly lived', wrote Debord, 'has become mere representation.' Nowhere is this dictum more starkly illustrated than in the case of Che, who, in the four decades since his death, has been used to sell everything from china mugs to denim jeans, herbal tea to canned beer. There was, maybe still is, a brand of soap powder bearing his name, along with the slogan 'Che washes whiter'. Today, Che lives! all right, but not in the way he or his fellow revolutionaries could ever have imagined in their worst nightmares. He has become a global brand.

The late Alberto Korda - whose iconic photograph of the bearded and long-haired Che wearing a beret with a red star may be the most appropriated image ever - won a moral victory of sorts when he successfully sued a British advertising agency for using it in an ad for Smirnoff vodka. The appropriation, though, is unstoppable, and radical chic was elevated to a new level of absurdity when Madonna recently dressed up as Che for the cover of her single 'American Life'. As I write, Korda's image is being debunked in the poster for Politics, Ricky Gervais's stand-up show, which sees the creator of The Office sporting a beret, beard, fatigues and fake tan. Had he wanted a real one, he could have booked a holiday with 'Che Trails', which offers trips to Cuba where you can 'follow in the footsteps of the famous revolutionary'.

'Ironically, Che's life has been emptied of the meaning he would have wanted it to have,' asserts Jorge Castañeda, author of Compañero: The Life and Death of Che Guevara . 'Whatever the left might think, he has long since ceased to be an ideological and political figure.' Castañeda insists, though, that Che still possesses 'an extraordinary relevance. He's a symbol of a time when people died heroically for what they believed in. People don't do that any more.'

Hitchens, too, believes that Che endures not because of how he lived, but how he died. 'He belongs more to the romantic tradition than the revolutionary one. To endure as a romantic icon, one must not just die young, but die hopelessly. Che fulfils both criteria. When one thinks of Che as a hero, it is more in terms of Byron than Marx.'

The myth of Che the romantic hero is about to enter a new phase with the release of The Motorcycle Diaries , a rose-tinted road movie based on the book the pre-revolutionary Ernesto Guevara wrote about his journey across Latin America in the company of his best friend, Alberto Granado. Directed by Walter Salles, who made Central Station and produced City of God, it comes trailing critical plaudits from this year's Cannes film festival. If, as the historian Robert Conquest once claimed, the cult of Che among the young is based on 'one of the unfortunate afflictions to which the human mind is prone... adolescent revolutionary romanticism', Salles should have a sure-fire hit on his hands. The presence of Hollywood's hippest heartthrob, Gael García Bernal - star of Amores Perros and Almodóvar's Bad Education - in the lead role will ensure that an impressionable new generation will discover Che, albeit as a tousled, sun-kissed loveable rogue on a road trip to political epiphany.

'The Che of The Motorcycle Diaries is more akin to Jack Kerouac or Neal Casady than Marx or Lenin,' says the film's producer, and former head of FilmFour, Paul Webster. 'He was naturally drawn to the peripatetic lifestyle that defined the Fifties and Sixties, that sense of constant motion and adventure that began with the Beats. Walter's film gives you a glimpse of the young, idealistic Ernesto Guevara before he became Che, the legend.' Webster wouldn't have been so keen to finance a film about the young Fidel Castro, then? 'No. There is no myth around Castro. Che was young and beautiful, and that, as much as all that happened later, is what underpins the myth. Paul Newman once said, "If I'd been born with brown eyes, I wouldn't be a film star." Well, if Che hadn't been born so good-looking, he wouldn't be a mythical revolutionary.'

At least two other films about Guevara are currently in development, one directed by Steven Soderbergh, and rumoured to star Benicio del Toro, the other a vehicle for Antonio Banderas, who has already played Che in Evita. Hollywood has flirted with the notion of the romantic revolutionary before, most notably in Spike Lee's flawed bio-pic Malcolm X and in Neil Jordan's confused portrait of Irish Republican Michael Collins. The late Marlon Brando made a less than convincing Zapata in Viva Zapata! in 1952. More recently, Oliver Stone made a controversial hagiographic documentary about Fidel Castro. Its release was put on hold when, in April, Castro executed three Cubans who had hijacked the ferry, and sentenced 78 dissident writers to 28 years in prison.

Unlike Salles, Soderbergh will have to tackle the contradictions of Che's revolutionary life, and show the ruthless guerrilla leader as well as the romantic pin-up. With all Hollywood's powers of persuasion, it is difficult to see post-9/11 US audiences taking to a gun-toting Communist guerrilla fighter preaching anti-American, anti-capitalist rhetoric, and calling for 'a dozen Vietnams'.

Hollywood's sudden renewed interest in Che - he was lionised once before in a best-forgotten 1969 epic Che!, starring Omar Sharif opposite Jack Palance as a fiendish Fidel - backs up Hitchens's view that while Guevara's ideological cachet may be at an all time low, his status as both sex symbol and heroic victim is undiminished. Once dubbed 'the poster boy for the revolution' by the right, Che was transformed into a global pin-up at the very moment of his greatest triumph, when Korda, a fledgling fashion photographer, snapped him standing beside Castro on a balcony in Havana on 5 March 1960.

'Finding Che in his lens,' writes Jon Lee Anderson, in Che Guevara: A Revolutionary Life , 'Korda focused and was stunned by the expression on Che's face. It was one of absolute implacability. He snapped and the photo soon went around the world, eventually becoming the famous poster that would adorn so many college bedrooms. In it, Che appears as the ultimate revolutionary icon, his eyes staring boldly into the future, his expression a virile embodiment of outrage at social injustice.'

The die was cast. By 1970, that defiant image had become, as the British pop artist Peter Blake later put it, 'one of the great icons of the 20th century', appearing on T-shirts, badges and postcards, a secular version of the holy pictures and relics of Catholic saints. The same image was silk-screened by Andy Warhol, and took its place alongside Marilyn Monroe and James Dean in the iconography of Pop Art. The transformation from symbol of violent revolution to emblem of Sixties cool was complete, and Che has remained more Lennon than Lenin ever since.

'The image of Che was just so right for the time,' says liberal American writer Lawrence Osborne, whose critique of Guevara appeared recently in the New York Observer. 'Che was the revolutionary as rock star. Korda, as a fashion photographer, sensed that instinctively, and caught it. Before then, the Nazis were the only political movement to understand the power of glamour and sexual charisma, and exploit it. The Communists never got it. Then you have the Cuban revolution, and into this void come these macho guys with their straggly hair and beards and big-dick glamour, and suddenly Norman Mailer and all the radi cal chic crowd are creaming their jeans. Che had them in the palm of his hand, and he knew it. What he didn't know, of course, was how much that image would define him.'

Osborne sees Che's iconographic status as being maintained in part by 'the absence of questioning voices addressing the darker side of the man and his ideology'. In Guevara's political writing he detects a 'puritanical zeal and pure and undisguised hatred' that, in places, becomes almost pathological. 'This was a guy who preached hatred, who wrote speeches that were almost proto-fascist,' he says, quoting a speech that ends, 'Relentless hatred of the enemy impels us over and over, and transforms us into effective and selective violent cold killing machines.'

Osborne points to the contradiction between the Che who spouted such rhetoric, and the Che who has been elevated to the level of secular saint. 'The right got it wrong when they called him a poster boy for the revolution. Che was much more than that - he was a steely, driven, ruthless leader. He may have been an idealist, but he was also someone unafraid to get his hands dirty in pursuit of an ideal. His contradictions define him more than anything else'.

From the start, Ernesto Guevara - the nickname Che came later from his habit of referring to everyone as che, or 'pal' - was a magnetic and strong-willed presence. Born in 1928, to aristocratic but radical parents in Rosaria, Argentina, he was the first of five children. His character was forged in part by the chronic asthma that would dog him until his death.

'His battle with asthma had much to do with what he became,' says Castañeda. 'As a child he grew used to resisting and overcoming a terrible illness through sheer will, and came to the conclusion early on that every problem could be solved or defeated through sheer will, even America, even global capitalism. That, in a way, was his strength and his downfall.'

Che's mother, Celia, from whom he inherited his indomitable spirit, and with whom he corresponded throughout his life, inculcated in him a free spirit and a passionate hatred of the Peronist right in Argentina. With her encouragement, he studied medicine in Buenos Aires, interrupting his education to undertake the motorcycle trip that politicised him.

In The Motorcycle Diaries, he describes the exploitation and poverty he sees everywhere, which he identifies as 'the living representation of the proletariat in any part of the world'. By the book's end, his anger has turned to hatred. 'I feel my nostrils dilate,' he writes, 'savouring the acrid smell of gunpowder and blood, of the enemy's death.' Youthful posturing maybe but, as his later life showed, Che had a cold-blooded streak as well as a love of battle.

In 1954, having seen the CIA-backed coup overthrow the socialist government in Guatemala, Che fled to Mexico, where he met the exiled Fidel Castro, who was plotting revolution against the Cuban dictator, Fulgencio Batista. Che immediately volunteered his services as a medical officer and, while training with Castro's guerrillas in Mexico, married his first wife, Hilda Gadea. Their daughter, Hildita, was just one year old when Che set sail for Cuba with Castro and 80 other exiles, and began the guerrilla campaign against Batista.

Initially, the campaign was a catalogue of disasters but slowly the rebels gained local support, often from peasants who realised it was more dangerous to support Batista than Che. 'Denouncing us put them in danger,' he wrote in his Cuban war diaries, 'since revolutionary justice was speedy.' In 1958, in a battle that has now entered Cuban folklore, a few hundred rebels defeated 10,000 of Batista's men in the Sierra Maestra mountains, and Castro and Che's impossible adventure sud denly turned into a real revolution. By the time they took Havana in 1959, Che had taken up with the woman who would become his second wife, 24-year-old Aleida March de la Torre. Politically, Aleida and Che were incompatible as she belonged to an anti-Communist revolutionary faction that he hated. But, as Jon Lee Anderson notes, 'When it came to women, especially attractive women, Che tended to put his political philosophies on hold.'

In truth, though, the same kind of contradictions attended those politic philosophies. Che was an inspiring leader but also a harsh and unbending taskmaster, who meted out stern punishment. On his orders, several peasants were executed for disloyalty, as were local bandits who preyed on the poor. Others, often no more than boys, underwent mock executions. 'We blindfolded them,' he wrote later, 'and subjected them to the anguish of a simulated firing squad.'

In his trenchant short study, Che Guevara, the British historian Andrew Sinclair concludes that, during the guerrilla war, Che 'discovered a cold ruthlessness in his nature. Spilling blood was necessary for the cause. Within two years, he would order the death of several hundred Batista partisans at La Cabana, one of the mass killings of the Cuban Revolution.' Later too, after the botched Bay of Pigs invasion by anti-Communist Cuban exiles, all the survivors were summarily shot.

In the halcyon post-revolution days, Che was made Governor of the National Bank, his face appearing on the two peso note. Magnum photographer Rene Burri - he took another defining photograph of Che, eyes blazing, cigar clamped in the side of his mouth - tells this story about the haphazard creation of Castro's first cabinet. 'One of Castro's aides asked, "Is there an economist in the room?", and, to everyone's surprise, Che stuck up his hand. Because they were all in awe of him, they voted him governor of the bank. It turns out Che had misheard the question. He thought the guy had asked, "Is there a Communist in the room?"'

Che did not last long in the post, and was soon made Minister for Industry, a job that made him a nomadic ambassador for the revolution. During the Cuban Missile Crisis in 1962 Che was more bullish even than Castro or Khrushchev, seemingly unconcerned that the whole world was holding its breath over the outcome. 'The worst thing I heard about him,' says Hitchens, 'is that he was in favour of launching the missiles. That, for me, is a contradiction too far. You can't be a great revolutionary who wants to free the world and be a guy who wants to push the button. You can only be one or the other.'

Rene Burri photographed Che in Havana in 1963, just months after the Cuban missile crisis. Che was being interviewed by an American woman from Look magazine. 'I was in his tiny office for three hours, the blinds closed throughout, and Che was pacing the room like a caged tiger. The interview was like a cockfight between Communism and capitalism, and he was strutting and angry, hectoring this woman, and chomping on his cigar. Suddenly, he looked straight at me and said, "So, you are with Magnum. If I catch up with your friend Andy, I'll cut his throat", and he drew his finger slowly across his throat.' Andy was Andrew St George, another Magnum photographer, who had travelled with Che in the Sierra Maestra, and then later filed reports for American intelligence. 'Che was fired up that day' says Burri, 'and he was maybe a showman, but it scared the hell out of me. I knew then, this was a man who was not cut out to be a politician, he was a soldier and a killer.'

By 1965, Burri had been proven right, and Che, fed up with the difficulties of trying to make post-revolutionary Cuba work, left the island to pursue armed struggle elsewhere, convinced that he could be the catalyst for countless revolutions in Africa and Latin America.

'There is a sense, seldom articulated, that Che, for all his heroism and romance, was a wild card, and that even Castro realised this relatively early on,' says Lawrence Osborne. 'He had this Jack London-style attitude to revolution as one great big unending adventure, but none of the political maturity to deal with the practical realities of making the country work. He had this Castilian Spanish upper-class guilt about the working class and peasants that he never quite overcame. For all the noble impulses that drove him, and I think there were many, Che's whole life could be read as a foredoomed attempt to leave his own class.'

In 1965, Che's adventurism and ideological zealotry led him him to Africa, and an unsuccessful attempt at revolution in the Congo. From there, he returned briefly to Cuba, whence, increasingly estranged from Castro, he set off for Bolivia to begin his last and final guerrilla war. Of all the books written by Guevara, The Bolivian Diaries are the most powerful and affecting, not least because the ideological demagoguery of old has disappeared, replaced by a more stoical voice. It is a diary of struggle and hardship, of dismay and defeat, the antithesis of The Motorcycle Diaries, and, of course, not a story that Hollywood will ever tell.

He was captured at the Yuro Ravine in 1967 by troops loyal to military President Barrientos. Over the phone from Mexico, Castañeda tells me that he is certain Castro had a troop of men ready to go to Bolivia as soon as he heard that Che was in danger, but that the Soviet deputy, Kosygin, just returned from conciliatory talks with US President Johnson, overruled such an action. 'Johnson made it clear to Kosygin that the Americans would countenance no attempts to save Che.'

Could Castro have saved Che, but chose not to? 'I don't think it's that simple. Real politics had intervened.But Castro always had the option to mount a rescue mission even if it was by no way assured. Put it this way: there had been a time, not long before, when he would have done it without question.'

The day after his capture, bedraggled and exhausted, Che was trussed up and taken to a thatched school house in La Higuera, where he was shot four times by a Bolivian volunteer called Mario Teran, who lives in hiding to this day. Che was 39. His last words were, 'I know you have come to kill me. Shoot, coward, you are only going to kill a man.'

But even his enemies knew that Che Guevara's legend would not die with him. To leave the world in no doubt of his identity, his captors instructed some local nuns to wash his face, tidy his bedraggled hair and beard, then photographed his corpse. To their dismay, the image that was circulated throughout the world recalled countless Renaissance paintings of the dead Christ taken down from the cross - and so Che attained iconic status for the second time.

'The Christ-like image prevailed', wrote Jorge Castañeda in Compañero. 'It's as if the dead Guevara looks on his killers and forgives them, and upon the world, proclaiming that he who dies for an idea is beyond suffering.'

Of course it is this ultimate sacrifice that defines the romantic myth of Che Guevara as much as his good looks or his revolutionary life. In death, he was frozen forever, and spared the ignominy of a long decline. 'Che's iconic status was assured because he failed,' says Hitchens, 'His story was one of defeat and isolation, and that's why it is so seductive. Had he lived, the myth of Che would have long since died.'

Jorge Castañeda agrees: 'What he shows us is that myths are bigger than mere politics or ideology, are bigger even than the cruel drift of history.' Che lives, then, and, as long as we do not look at his life too closely, will live on as long as we need him to, and in whatever way we want him to. For him, one suspects, that would have been the cruellest fate imaginable.

· The Motorcycle Diaries is released on 27 August.