Thieu collapsed at his home in suburban Foxboro on Thursday, and died late Saturday at Beth Israel Deaconess Medical Center in Boston hospital, according to his cousin, Hoang Duc Nha. His death also was confirmed by Chau Tran, former secretary general of South Vietnam's House of Deputies.
Thieu assumed power in 1965 and presided over the U.S.-backed South Vietnam until the fall of its capital city, Saigon, in 1975, to Communist-led troops from North Vietnam.
He then largely disappeared from public view and lived quietly in exile, first in London, then in the Boston area. He remained, however, an enduring symbol of the futility of a war in which nearly 60,000 American troops died.
With North Vietnamese closing in on the South Vietnamese capital of Saigon, and the war all but officially lost, he still declared: "We will fight to the last bullet, the last grain of rice."
Even with the assistance of 500,000 U.S. troops and massive amounts of military aid, he was never able to turn the tide against the Communist North.
He left power defeated, despised and bitterly denouncing the superpower nation that had befriended him for more than a decade.
He claimed the United States broke a promise to continue to provide military support after pulling out its combat troops in 1973, and that, he said, "led the South Vietnamese people to death."
When the end did come, his resignation was demanded by all sides, including his former allies in the United States, to make way for peace talks with the North Vietnamese.
Thieu reluctantly stepped down on April 21, 1975, and left the country, but the talks never came. South Vietnam was overrun shortly after his departure.
A shrewd politician and brilliant military strategist, Thieu maneuvered himself from the bloody battlefield to the highest seat of power in his country.
Born in a southern coastal fishing village, Thieu became involved as a youth in the national liberation movement led by Ho Chi Minh, who went on to become president of North Vietnam. Thieu, however, grew disillusioned and eventually switched sides.
He established himself early in his career as a cautious, yet reliable, combat officer. He was one of the key participants in the overthrow of the Diem regime during the early 1960s.
The same year that he rose to the nation's highest office in 1965, holding the ceremonial post of chief of state, President Johnson ordered the first major escalation of the war, sending more than 100,000 U.S. troops to Vietnam.
In September 1967, Thieu was elected to the presidency after pulling off a stunning switch with his rival, Prime Minister Nguyen Cao Ky, who had previously wielded the most influence in the South Vietnamese military regime.
Thieu's entry into office initially brought stability and unity to a cuntry in political chaos. In the years that followed, Thieu ruled with an iron hand, moving with the same caution as he had on the battlefield. He made decisions alone or with the advice of only one or two trusted aides and swiftly crushed any dissent.
Several years later, his country's deteriorating economic situation, as well as corruption charges against his regime, but not necessarily against Thieu himself, left him scrambling to stay in power.
What proved most costly, however, was a series of costly military mistakes that left the South Vietnamese army on the run and the fall of South Vietnam imminent. Soon, the clamor was that only Thieu's resignation would appease the North Vietnamese and stave off the impending blood bath.
In the years after the war, Thieu shunned almost all requests for interviews. He re-emerged nearly two decades later in 1992 to denounce rapprochement between the United States and the Communist government in Vietnam.
But a year later, his tone had changed. Thieu spoke of his willingness to take part in national reconciliation talks that would allow members of the Vietnamese exile community to go home. The Vietnamese showed no interest in having him act as a go-between.
© MMI The Associated Press. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed