Born in 1930 near Hanoi and raised by an aunt, Nguyen Cao Ky joined the Communist resistance to French colonial rule at the age of 16, inspired by Ho Chi Minh. He fell ill with malaria, and when he recovered he was drafted by the French-controlled government, which sent him abroad to train as a pilot, though he never saw combat.

When the country was divided in 1954 after the French defeat at Dien Bien Phu, he fled south along with hundreds of thousands of others and joined the American-backed South Vietnamese Air Force.

In 1965, when he was 34 and a commander of the air force, he was chosen by his fellow military officers to lead the country as prime minister, ending a cycle of coups and countercoups that followed the 1963 assassination of Ngo Dinh Diem. In his book, Mr. Ky quotes an assessment of him by the State Department official William Bundy that he was “the bottom of the barrel” and the last choice for the job.

In power, he made a show of cracking down on corruption, executing one businessman accused of war profiteering, and he threatened to kill dissidents, opponents and bomb units led by rival officers, and he suppressed a Buddhist-led uprising in 1966.

After fleeing to the United States, Mr. Ky fended off accusations of corruption himself. Responding in 1984 to the columnist Jack Anderson, who accused Mr. Ky of being involved with criminal gangs, he said: “If I had stolen millions of dollars I could live like a king in this country, but obviously I don’t live like a king.”

In his book he made light of his struggles to make a new life in America.

“When a former national leader becomes a storekeeper, it is news,” he wrote. “Journalists of every sort visited my store. One day a bus driver came in to ask if his passengers, German tourists, could enter and see me. I discovered that my business was a standard stop on his tour, which ended at Disneyland.”