Dr. Trần Kim Tuyến (1925–1995) was the chief of intelligence of South Vietnam under its first President Ngô Đình Diệm from 1955 to 1963. As a Roman Catholic, he was trusted by the Ngô family, and was part of their inner circle. Tuyến was responsible for a variety of propaganda campaigns against communists, and was prominent in operating the secret Cần Lao party apparatus which maintained the Ngô family's rule. In the course of his work, Tuyến emulated the tactics of the communists. He eventually became disillusioned and plotted against the regime before being exiled. After Diệm was deposed, Tuyến returned to South Vietnam, but the military junta which had replaced the Ngô family jailed him for five years. He fled the country in 1975 as Saigon was falling.
Tuyen hailed from Phát Diêm, Ninh Bình Province, Vietnam, French Indochina. He studied at the French-founded university in Hanoi, obtaining degrees in law and medicine. As a university student, he had protested against the French colonial administration's control over Vietnam's Catholic clergy, landing him in trouble with the police.
However, his religious convictions caused him to spurn the Hồ Chí Minh-led Viet Minh independence movement, which was strongly atheist. Although he was ambitious, Tuyến was aware of his provincial accent and his manner of stumbling over long words, which was not considered to be consistent with the archetypal leader with a city accent. In 1946, while still a student, Tuyến came to know the Ngô family by chance. His future mentor Ngô Đình Nhu wanted to travel from Hanoi to a Catholic area near the border with Laos and needed a guide. A Catholic priest asked Tuyến to lead the way on a bicycle while Nhu followed in a covered cyclo to evade French colonial and Vietminh attention.
In mid-1954, at the time the Geneva Conference had concluded, Tuyến had been working for the anti-communist Vietnamese National Army of the State of Vietnam in an outlying province, only travelling to Hanoi during the weekends. As a result of the discussions in Geneva, Vietnam was to be temporarily partitioned pending national reunification elections in 1956. In the meantime, the Vietminh controlled the Democratic Republic of Vietnam in the north, and the State of Vietnam was handed the south. The agreements also allowed for the free passage of civilians between either side for 300 days, while military personnel were obliged to move to their respective zones. Tuyến had persuaded a substantial number of northern Catholics to leave their homes and move south. As a result, he later tried to persuade Diệm to maintain some contact with members of the communist regime in Hanoi in the hope of persuading them to defect.