Ta Mok(meaning grandfather Mok) was born in 1926 in Takeo province, Cambodia. His birth name was Chhit Choeun. Former Buddhist monk and student at the Pali High School in Phnom Penh, Ta Mok, was actively involved in the 1940s resistance movements against the French and the Japanese. Later, he joined the Cambodian Communist Party (CPK). His activity was concentrated in the southwest zone of the country. He was nominated member of the Central Committee of the Cambodian Communist Party in 1963.
In 1968, he became Secretary of the southwest zone, a post that provided the platform for his election as member of the Standing and Military Committees of the Central Committee. These positions afforded Ta Mok the de jure and de facto authority to direct the conduct of CPK subordinates, in particular those in the southwest zone.
Ta Mok, consequently, held important military functions in the Khmer Rouge Movement (he became Commander in Chief of the Army in 1977). As Party Secretary for the southwest zone, he orchestrated major purges: in the Angkor Chey district and was said to have had 30’000 people massacred. Ta Mok’s own appointees then progressively began to replace those senior party members who were removed for collusion with Viet-Nam. In this way the party cadres of the south- west became the spear head of the revolution. After the fall of the Khmer Rouge following the Vietnamese invasion in December 1978, Ta Mok became the Supreme Military Commander of the remnants of the Khmer Rouge and commanded the guerrillas from his fiefdom of Along Veng in the north. In the spring of 1998, at a final gathering, the remaining units of the Khmer Rouge obliged him to seek safety in the dense forests which separate Cambodia from Thailand.
He was arrested on 6 March 1999 close to the Cambodian border, just inside Thai territory, and afterwards transferred by helicopter to a prison in Phnom Penh. At the time of his arrest, and for several decades before, “Grandfather Mok” had maintained a network of business contacts and commercial transactions with Thailand.