Ta Mok, military commander of the Cambodian Khmer Rouge movement, was responsible for the deaths of thousands of people during the Pol Pot regime of the late 1970s.
Ta Mok: Last leader of the Khmer Rouge
Born in 1926, he was named Chhit Choen and trained as a Buddhist monk at Pali High School in Phnom Penh.
During the 1940s he was an active opponent of both French colonial rule and the Japanese occupation.
Joining the Cambodian Communist Party, he rose to become a member of its Central Committee, and commanded its forces in the south-west of Cambodia.
Under the alias Ta Mok - uncle Mok - he served as the Khmer Rouge's chief of staff, after having been a member of the Kymer Issarak movement, and lost part of a leg in combat in 1970.
During the Vietnam war, Cambodia's neutrality was fatally compromised. The Viet Cong used the country as a base from which to launch attacks into Vietnam.
And the United States began a secret bombing campaign in 1969, before briefly invading the country the following year.
By the mid-1970s, Cambodia was in civil war. The Khmer Rouge, which initially presented itself as a peace-loving and democratic organisation, finally took control of the country in 1975, renaming it Democratic Kampuchea.
Up to two million died in the 'killing fields'
With Pol Pot at its head, the five years of Khmer Rouge government saw up to two million people murdered.
In an ideologically-driven campaign against so-called "parasites" - intellectuals, city-dwellers and disabled people among them - mass genocide in "killing fields" became the order of the day.
Ta Mok, who became commander-in-chief of the army in 1977, was the driving force behind a number of purges. Massacres ascribed to him, including one of 30,000 people in the Angkor Chey district, earned Ta Mok the nickname 'Butcher'.
Late in 1978, Vietnam decided to act. Its forces invaded Cambodia, and the Khmer Rouge fled. Ta Mok went north, becoming supreme military commander of the remnant forces.
In 1997, following a split within the movement, Ta Mok became leader of one faction. He arrested Pol Pot, who was condemned to house arrest for life and who died in his custody in 1998.
Ta Mok was captured in 1999
After years of cat-and-mouse in the vast forests that separate Cambodia from Thailand, Ta Mok - the last major Khmer Rouge figure still at large - was finally arrested, inside Thai territory, on 6 March 1999.
Two days earlier, the United Nations had published a report which recommended the establishment of an International Criminal Court.
Transferred to Phnom Penh, Ta Mok was initially accused of membership of the now-banned Khmer Rouge before being charged with genocide and crimes against humanity.
If he had lived long enough, he would have been a key defendant in the trials of Khmer Rouge leaders, which are scheduled to begin in mid-2007.
Correspondents say his death deprives Cambodians of a chance to see justice done.