POL Pot, who has died aged 73, was the leader of the Communist Khmer Rouge in Cambodia from 1975 to 1979, and one of the most savage tyrants of the 20th Century.

Although Pol Pot's stage was much smaller than that of Hitler or Stalin, in abuse of power he was their equal. In nearly four years of Khmer Rouge misrule, more than 1.6 million Cambodians (about a fifth of the population) are believed to have been massacred or deliberately starved to death.

Whole cities and towns, which the regime considered to be breeding grounds of bourgeois mentality, were evacuated. The excuse given was that there was not enough rice to eat; the population were forced into the countryside to work in the fields, where many died. Having eliminated his internal "enemies", Pol Pot turned on Vietnam, thus providing his neighbour with the pretext for invasion and occupation. His legacy was a devastated population, an economy in ruins, and military defeat. He fled to the jungle, and was sentenced to death in absentia for genocide.

One of the few Westerners to meet Pol Pot while he was in power in Cambodia described him as having an attractive face, polished manners and a quiet, reassuring voice. Prince Norodom Sihanouk - now King Sihanouk, and at various times Cambodia's head of state - conveyed a similar impression: "We know that he is a monster but if you meet him he is nice. He is not ugly, and is a little fat. He is a man who smiles, speaks gently, quite unlike his image as a second Hitler."

In truth no one knew Pol Pot. He was one of the most reclusive despots in history, making few speeches and rarely giving interviews. Even the date of his birth has been a matter of controversy. It was only in September 1977, nearly two and half years after he had come to power, that he declared himself to his people as their leader. Until then they had been aware only that their destinies were governed by the anonymous and omniscient "Angkar" or "Organisation".

Determined that Cambodia should be self-sufficient, Pol Pot manifested a chronic mistrust of foreigners. He and his henchmen liked to believe that they had achieved power in 1975 entirely through their own efforts. But in fact North Vietnam bore the brunt of fighting against Lon Nol's rival army in the early 1970s; and once the Khmer Rouge had won, China propped up their regime.

Pol Pot became obsessed with eliminating those whom he considered not true Khmers - Vietnamese, Chams, Thais, Chinese and Laos. Race was even more important than class in the Khmer Rouge's genocidal quest for total control. Pol Pot was born Saloth Sar in January 1925, by his own account. His family were landowners in the central province of Kompong Thom.

After six years at a Buddhist school in Phnom Penh, young Sar failed to pass his exams, and returned to his family in the country. He received his secondary education in Kompong Cham, and in 1944 was back in the capital studying carpentry at a technical school. After the Second World War, the French, the colonial power in Indo-China, allowed the formation of political parties in Cambodia. Three were formed, and Saloth Sar was attracted to the moderate Democratic Party, which won the 1946 elections.

In 1949 he travelled to Paris on a scholarship and enrolled at the Ecole française de radio-électricité, where, once again, he failed to pass his exams. But the years in France set him on his revolutionary course. He joined the French Communist Party, and became a leading member of the Left-wing Cambodian élite in France. Under the pseudonym "Original Khmer", Sar contributed to the review Cambodian Student; he attacked Prince Sihanouk, and advocated the abolition of the monarchy and the establishment of democracy.

One of his fellow students was Ieng Sary, later to be his right-hand man. Sary arrived in Paris a year after Sar, and while there married Khieu Thirith. Through them Sar met Thirith's elder sister, Khieu Ponnary; both had their scholarships suspended for political agitation. In 1953 they returned to Cambodia, and were married.

Once back home, Sar joined the struggle for independence from France. After the defeat of the French in 1954 and the assumption of complete control over independent Cambodia by Sihanouk, Sar was one of the few Communists allowed by the Party to remain in the country, rather than retreat to North Vietnam. He took a job in order to disguise his political affiliations, and became active for the newly formed Left-wing Pracheachon Party in the 1955 elections.

Sihanouk's Sangkum Party won every seat, but the Communists continued their struggle. They opened their own lycée, at which both Sar and Sary taught, and tried to organise workers in the capital. In 1960 the first party congress of the Cambodian Communists was held in empty railway trucks at Phnom Penh station.

They adopted statutes, took the name of the Workers' Party of Kampuchea, and elected a central committee on which Tou Samouth occupied top, and Sar third, position. Three years later Samouth mysteriously disappeared and Sar took his place as leader. Fearing elimination at police hands, Sar and nearly all the central committee left Phnom Penh for the jungle.

The spark for armed conflict came in 1967 when peasants revolted against the attempts by Lon Nol, Sihanouk's Prime Minister, to force them to sell rice to the government at low prices. Sar and his followers moved from the eastern plains to the hills of the north-east, and in 1968 launched the first offensive of their guerrilla war.

In 1970 Lon Nol overthrew Sihanouk in a coup d'état, and the Prince became titular head of the Khmer Rouge, though Sar and his colleagues held all the power. This arrangement, which gave the Communists unmerited respectability, was to continue after their victory in 1975. Already the Khmer Rouge had begun the "purification" campaigns. In 1971 they struck at Vietnamese living in areas under their control in eastern Cambodia, and then at Cambodian Communists who returned from training in Vietnam.

Militarily, their strength rose from about 5,000 in 1967 to 68,000 when they finally took Phnom Penh in 1975, 13 days before the fall of Saigon to North Vietnam. By that time the party had around 14,000 members. Because of their small numbers and lack of support in Phnom Penh, the Khmer Rouge immediately evacuated the population from the capital and scattered them around the countryside. This was the first and most dramatic step in the systematic terrorising of Cambodia.

In early 1976 Sihanouk, allegedly still head of a united front government, approved a new constitution which abolished the monarchy and religion. Having done what was required of him, he was placed under house arrest. The Khmer Rouge then moved against those it considered to be its enemies, beginning with officials of the old regime, then ethnic minorities and, finally, its own members, in particular those in command of the zones into which Cambodia was divided.

It was from the Eastern Zone that Heng Samrin and others, including Hun Sen, now Prime Minister, escaped to Vietnam, thus enabling the establishment of a Cambodian Communist front against Pol Pot, as Sar had now become. Samrin was to head the government in Phnom Penh after the Vietnamese invasion. Fighting between Cambodia and Vietnam had broken out in the middle of 1977. By spring the next year the Vietnamese leadership had decided to invade Cambodia and remove Pol Pot. It launched its offensive on December 22 and took Phnom Penh just over two weeks later.

Pol Pot retreated to the Thai border with his loyal followers and once again found himself fighting a guerrilla war. The new government in Phnom Penh sentenced him to death in absentia for genocide, and in December 1979 he was replaced as Prime Minister of "Democratic Kampuchea" by Khieu Samphan, who became the front man for the Khmer Rouge. In 1982 the Khmer Rouge and factions led by Prince Sihanouk and Son Sann, a former minister and governor of the national bank, joined forces to oppose Heng Samrin and his Vietnamese backers in the Coalition Government of Democratic Kampuchea. Samphan was the coalition's vice-president and foreign minister, and there were rumours that he had quarrelled with Pol Pot over redefining Khmer Rouge ideology.

In 1991 Samphan signed the Cambodian peace treaty in Paris for the Communists, but they later refused to disarm, and boycotted the 1993 elections held under United Nations supervision. Pol Pot was rumoured to have received treatment, in 1985, for high blood pressure, malaria and other ailments, in a Peking hospital. The same year it was announced that he had retired as commander-in-chief of Khmer Rouge forces, which were the biggest of the three Cambodian guerrilla groups, and estimated at that time to number about 30,000. The news was treated with scepticism by the outside world.

A Khmer Rouge guerrilla commander who defected in 1995 said Pol Pot gave the order for the kidnapping of three British, French and Australian backpackers in Cambodia the previous year. They were later killed. Pol Pot himself remained as reclusive as ever. After being interviewed by a Japanese journalist at a guerrilla camp in 1979, he was not seen by a foreigner until 1997. By then the Khmer Rouge had split between the northern forces under Pol Pot and the western, under Ieng Sary, his brother-in-law.

After he had ordered the killing of Son Sen, his old comrade, and his family, Pol Pot was arrested by the one-legged Ta Mok, the military commander. In July a "people's tribunal" sentenced Pol Pot to life imprisonment. Later that year, in an interview with the Far Eastern Economic Review, Pol Pot was largely unrepentant about the devastation which the Khmer Rouge had visited on Cambodia. He said: "I do not reject responsibility - our movement made mistakes, like every other movement in the world. But there was another aspect outside our control - the enemy's [the Vietnamese] activities against us."

In a reference to part of the old Khmer empire seized by Vietnam in the 17th Century, he said: "I'm quite satisfied on one thing: if we had not carried out our struggle, Cambodia would have become another Kampuchea Krom in 1975." Pol Pot also claimed that Tuol Sleng, the notorious detention centre in Phnom Penh, was a piece of Vietnamese propaganda.

Earlier this month President Clinton ordered plans to be drawn up for his arrest and trial before the international tribunal in The Hague. By then Pol Pot was dying and the movement he had dominated, weakened by defections to the Cambodian government, was fighting for survival.