Nguyen Van Thieu
Nguyen Van Thieu (1923–2001) was a South Vietnamese general and, at various times, head of military governments, then president of South Vietnam 1967–1975.
As a colonel, he was part of the coup that overthrew President Ngo Dinh Diem in 1963. Afterwards, he became chairman of the ruling military junta's National Directory, then chief of state in 1965. 
Thieu won an 1967 election with Nguyen Cao Ky, after Thieu to ban Ky, internal U.S. documents emphasized the need to include opposition. Phan Quang Dan, Tran Van Huong, and Nguyen Luu Vien were specifically mentioned. 
Search for coalition
As Vietnamization forced South Vietnam to be more on its own,in May 1969, he created a National Social Democratic Front, in search of a new political solution  Thieu and the NLF found one another unacceptable to form a coalition, although it was postulated that a broader coalition, including some of the significant minorities such as the Montagnards, Cao Dai, a Catholic broad front to be organized, and Hoa Hao might be more viable. Such a coalition would require U.S. withdrawal.
He won the presidency again in 1971 in a rigged election.
Fall of South Vietnam
In 1975, he released assurances dated April 1973, from President Nixon that the U.S. would "react vigorously" if North Vietnam violated the truce agreement. But Nixon had resigned in August 1974 and his personal assurances were meaningless; After Nixon made the promises, Congress had prohibited the use of American forces in any combat role in Laos, Cambodia, and Vietnam without prior congressional approval. This was well known to the Saigon government.  The Ford Administration, with specific legislative restrictions against direct aid and a lack of public support, was limited to some fnancial aid. remained in the post until April 21, 1975, when he resigned and fled the country as North Vietnamese troops rushed toward Saigon. Duong Van Minh actually was the last President, who was arrested and imprisoned by the North Vietnamese when Saigon fell.
- Butterfield, Fox (October 1, 2001), "Nguyen Van Thieu Is Dead at 76; Last President of South Vietnam", New York Times
- "South Viet Nam: No Longer a Choice", Time, September 13, 1971
- William J. Jorden (National Security Staff), [Foreign Relations, 1964-1968, Volume V, Vietnam 1967 Memorandum to Assistant to the President for National Security Affairs Walt Rostow, "Priorities in Viet Nam under a New Government], Document 304
- Hickey, GC, Accommodation and Coalition in South Vietnam, Rand Corporation
- "Seeking the Last Exit from Viet Nam", Time Magazine, April 21, 1975