Pol Pot, leader of the Khmer Rouge, was one of the most reviled figures of the 20th century. In his four years as Prime Minister of Democratic Kampuchea, he tried to remake an impoverished South-East Asian nation into a model of radical Maoism.

His paranoia and brutality sent it into a chasm of darkness in which as many as two million died. Pol Pot's enduring legacy is the thousands of mass graves that litter Cambodia, but he was chillingly unrepentant up to his death at 73, saying recently that his "conscience was clear".

Scholars will long debate what drove a man described by those who knew him as gentle and unassuming to create a system under which family life was erased, children became torturers, and even loyal followers of the regime were bludgeoned to death in their thousands.

Pol Pot came to power in April 1975 and set about creating what the Khmer Rouge saw as a rural Utopia without money, or private property. The cities were emptied and Cambodia's history began again at Year Zero.

There are few clues in his childhood to explain the violence he unleashed in later life. His father was a moderately wealthy farmer and his mother had connections at the royal court in Phnom Penh. At the age of six he was sent to the city for his education and later attended a boarding school for bright students.

In 1948 he was among the first students sent on government scholarships to go to university in France.

His political ideas began to form in Paris where he aimlessly studied radio engineering, failing to get a degree but becoming drawn to the optimistic vision of communism then circulating. In an interview in October 1997, Pol Pot said he began reading about the French revolution, spending his scholarship money on second-hand books and copies of the French Communist Party newspaper, L'Humanite.

Opposition to French rule in Vietnam, Cambodia and Laos was centred in the Indochina Communist Party, which attracted many students at the time. With Communist victories in China and across Eastern Europe, Marxism seemed the way to liberate Cambodia from the French. Pol Pot began to attend study sessions organised by the French Communist Party.

Another person who went to the meetings would later describe him as "the most intelligent, the most convinced, the most intransigent. It was he who animated the debates and most impressed the newcomers".

Pol Pot returned to Cambodia in 1953, just before the country won its independence under King Sihanouk, who abdicated to take up a position as head of government. It was at this time that his revolutionary fervor developed, he later said.

Shocked on his return by the poverty of his relatives, he was driven to political action. In 1956, he began teaching at a private college, where according to his biographer, David Chandler, he was remembered for his mild, affable manner and his knowledge of French literature. He was already leading a clandestine life in the Indochina Communist Party, building up networks of supporters. In 1960, Sihanouk, later Prince Sihanouk, launched a crackdown on the Communists during which the party's secretary, Tou Samouth, disappeared. Pol Pot stepped into his shoes and emerged as the head of the party's Cambodian section.

Accusations would later surface that Pol Pot had connived in Samouth's murder to clear his route to the top in what was his first act of political violence. Pol Pot, however, denied any role in the killing.

In 1963, he fled to the countryside to lead the resistance against Sihanouk. From then on, he would become Brother Number One, the shadowy head of the Communist Maquis on the run in camps in north-eastern Cambodia. In 1965, he went to Hanoi, where tensions were building with the Vietnamese. Pol Pot bristled at what he saw as their superior attitude and demands that the Cambodians hold off from armed struggle against Sihanouk until North Vietnam had won its war against the US.

He later went to China, where the Cultural Revolution was swirling. Pol Pot was said to have been impressed by Mao Zedong's vision of permanent revolution, his harnessing of young impressionable minds, and the destruction of all vestiges of history.

The armed struggle began in 1968 when Khmer Rouge guerrillas clashed with the army and police. The situation in Cambodia began to unravel, and in 1969 the United States began its secret bombing of Vietnamese bases in Cambodia.

At the beginning of 1970, Sihanouk left for his annual cure at a spa in France and was deposed by his chief general, Lon Nol. The new right-wing regime in Phnom Penh galvanised the Chinese and Vietnamese, previously only lukewarm supporters of Pol Pot, and they stepped up help.

Sihanouk was set up in Beijing as the nominal head of a united front against Lon Nol, while Pol Pot took command at a headquarters in north-eastern Cambodia. He had just a few thousand men under arms but with Vietnamese weapons and training they were becoming a more effective force. Vietnamese troops, tempered by years of war in their own country, held off offensives by Lon Nol.

US bombers took an enormous toll, beating back Khmer Rouge attacks on Phnom Penh in 1973. A year later the guerrillas formed a noose around the capital. Its population had swollen as people fled there to escape US bombings and the rigid social control imposed in areas under the Khmer Rouge.

The final assault on Phnom Penh began in the dry season in 1975. At the beginning of April, Lon Nol fled into exile and the US embassy was hurriedly evacuated. On 17 April, Pol Pot's silent soldiers, many of them just young teenagers in black pyjamas, arrived in the city and ordered all two million people to evacuate. In the intense heat, people were forced on to the roads on foot, families were separated in the crush, even hospital wards were savagely cleared. As far as the Khmer Rouge were concerned, they were all enemies.

Only when the city was empty did Pol Pot arrive to take over. He became Prime Minister in the shadowy Government that presided over a smouldering ghost town. He began to work on the four-year plan under which Cambodia would make its great leap forward to socialism by 1979. Rice yields would be tripled to three tonnes a hectare and a vast area would be planted in the malarial jungles of north-eastern Cambodia. Those forced out of the cities, known as "new people" because they were supposed to abandon all links with the past, were sent to these areas to dig canals and clear fields .

Hundreds of thousands died of disease, hunger and beatings. Of a population of seven million, as many as two million died. The Khmer Rouge cadres saw them as expendable, telling them: "Keeping you is no gain. Losing you is no loss."

Stubbornly ignorant of the realities of Cambodian agriculture, Pol Pot believed rice exports would finance his new vision of a developed Cambodia. Food production collapsed.

Believing that the family stood in the way of his radical vision of socialism, he tried to break down the capitalist structure by splitting families and forcing people to eat in communal halls.

Driven by the virulent Maoism of its isolated leaders and their vision of a racially pure country, the revolution destroyed everything Cambodians held dear, unravelling the connections of Buddhism, village life, friends and family.

By 1977, Pol Pot's paranoia had started to fuel a series of rampaging, self-destructive purges. The deaths and torture at Tuol Sleng, a school turned into an interrogation centre named S-21, would be one of the most macabre legacies. About 16,000 people, many of them Khmer Rouge cadres and their families, passed through Tuol Sleng, where they were photographed and their confessions kept in well-ordered files.

Tales of what was happening in Cambodia started to trickle out in 1977 through refugees fleeing to Thailand, but the closed country remained an enigma.

Western analysts were able to connect the fact that Solath Sar and Pol Pot were the same person only when he was photographed on a visit to Beijing. However, hidden by the secrecy, Pol Pot's regime was starting to unravel. Tensions were rising with the Vietnamese, who had sent troops across the border to retaliate for Cambodian massacres on their side.

In December, he cut relations with Hanoi and accused Vietnam of aggression. Hanoi, which had remained silent until then, began referring to his "barbaric, mediaeval policies."

On 25 December 1978, Vietnam sent 100,000 men across the border and quickly destroyed Cambodian defences. Sihanouk, who had spent the previous years under house arrest, was hustled out on a plane to Beijing less than 24 hours before the Vietnamese arrived in the capital.

Pol Pot fled to Thailand aboard a helicopter on the morning of 7 January 1979. That day marked the end of what Cambodians call "the era of the contemptible Pot". But it did not mark the end of his career. Supported by the Thai military, he was able to regroup on the frontier and rebuild some of his guerrilla units.

His rhetoric turned more to stirring up the ancient passions of Cambodian nationalism and the deep fear of being swamped by Vietnam. After 1981 he disappeared from public view.

Little is known about his personal life or personality other than descriptions of him as calm and charismatic. He married Khieu Ponnary, a teacher he met in Paris, in July 1956. A sombre, austere woman whose sister
was married to the Khmer Rouge leader Ieng Sary, she would eventually plunge into madness and spent much of the 1980s in a hospital in Beijing. Pol Pot married for a second time in the 1980s to a peasant woman in her 30s, called Sar. She bore him his only child, a daughter born in 1986.

After ordering the execution of one of his lieutenants, Son Sen, who he believed had tried to betray him, Pol Pot tried to flee but was captured and tried by his former supporters, not for crimes against humanity but for his role in the internal struggles of the Khmer Rouge.

His bizarre trial, at which crowds chanted slogans while he sat impassive and unmoved, was filmed by an American journalist, Nate Thayer, who later interviewed Pol Pot, his first contact with a Western journalist since the early 1980s.

The interview revealed his profound delusions and his intense hatred of the Vietnamese. He denied even knowing about the deaths at Tuol Sleng, which he described as an "exhibition" set up by the Vietnamese. He told Thayer that although the Khmer Rouge had made mistakes, their actions were justified by the threat of annexation from Vietnam.

"I came to carry out the struggle, not to kill people," he said. "My conscience is clear. As I told you before, they fought against us, so we had to take measures to defend ourselves."

Pol Pot spent his last months under house arrest in a wood and thatch hut. He was partially blind after a stroke in 1995. His books had been taken from him and he complained of boredom, although he was allowed a radio on which he listened to the Voice of America.

Although he talked about the deaths of his compatriots in a flat monotone, he was animated when discussing his health, according to Thayer. "You look at me from the outside. You don't know what I have suffered."

In 1987, he told a group of political students that as long as his followers continued the fight against the Vietnamese, he would "die peacefully". His weakened force of guerrillas are barely capable of fighting now. But Pol Pot leaves behind a country and people still recovering from his years. When Cambodian refugees from his terror arrived in the United States, some were blind. Doctors could find no physical reason for their loss of sight, which seemed to have been caused by intense trauma. Pol Pot's legacy was a country where people willed themselves to blindness rather than witness more of the agonies he wrought.

Robert Templer is Director of the Asia programme at International Crisis Group who work to prevent conflict worldwide

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