Nguyễn Cao Kỳ (listen; 8 September 1930 – 23 July 2011) was a Vietnamese military officer and politician who served as the chief of the Republic of Vietnam Air Force in the 1960s, before leading the nation as the prime minister of South Vietnam in a military junta from 1965 to 1967. Then, until his retirement from politics in 1971, he served as vice president to bitter rival General Nguyễn Văn Thiệu, in a nominally civilian administration.Born in northern Vietnam, Kỳ joined the Vietnamese National Army of the French-backed State of Vietnam and started as an infantry officer before the French sent him off for pilot training. After the French withdrew from Vietnam and the nation was partitioned, Kỳ moved up the ranks of the Republic of Vietnam Air Force to become its leader. In November 1963, Kỳ participated in the coup that deposed president Ngô Đình Diệm and resulted in Diệm's assassination.

In 1964 Kỳ became prominent in junta politics, regarded as part of a group of young, aggressive officers dubbed the "Young Turks". Over the next two years, there were repeated coup attempts, many of which were successful, and Kỳ was a key player in supporting or defeating them. In September 1964, he helped put down a coup attempt by Generals Lâm Văn Phát and Dương Văn Đức against Nguyễn Khánh, and the following February he thwarted another attempt by Phát and Phạm Ngọc Thảo. His favored tactic in such situations was to send fighter jets into the air and threaten large-scale air strikes, and given his reputation for impetuosity, he usually attained the desired backdown. After the latter attempt, he also had the weakened Khánh forced into exile and eventually took the leading position in the junta in mid-1965 by becoming prime minister, while General Thiệu was a figurehead chief of state. During his period at the helm, he gained notoriety for his flamboyant manner, womanizing, and risky and brash behavior, which deeply concerned South Vietnam's American allies and angered the Vietnamese public, who regarded him as a "cowboy" and "hooligan". He cared little for public relations, and on occasion publicly threatened to kill dissidents and opponents as well as to flatten parts of North Vietnam and South Vietnamese units led by rival officers with bombings, although none of this materialized.

Nevertheless, Kỳ and Thiệu were able to end the cycle of coups, and the Americans backed their regime. In 1966 Kỳ decided to purge General Nguyễn Chánh Thi, another officer in the junta regarded as his greatest rival, from a command role. This provoked major unrest, particularly in South Vietnam, where some units joined with Buddhist activists supportive of Thi and hostile to Kỳ in defying his junta's rule. Three months of large-scale demonstrations and riots paralyzed parts of the country, and after much maneuvering and some military battles, Kỳ's forces finally put down the uprising, and Thi was exiled, entrenching the former's grip on power.

In 1967, a transition to an elected government was scheduled, and after a power struggle within the military, Thiệu ran for the presidency with Kỳ as his running mate—both men had wanted the top job. To allow the two to work together, their fellow officers had agreed to have a military body controlled by Kỳ shape policy behind the scenes. The election was rigged to ensure that Thiệu and Kỳ's military ticket would win, and strong executive powers meant that junta, in effect, still ruled. Leadership tensions persisted, and Thiệu prevailed, sidelining Kỳ supporters from key military and cabinet posts. Thiệu then passed legislation to restrict candidacy eligibility for the 1971 election, banning almost all would-be opponents; Kỳ and the rest withdrew as it was obvious that the poll would be a sham; Thiệu went on to win more than 90 percent of the vote and the election uncontested, while Kỳ retired. With the fall of Saigon, Kỳ fled to the United States. He continued to heavily criticize both the communists and Thiệu, and the former prevented him from returning. However, in 2004, he became the first South Vietnamese leader to return, calling for reconciliation between communists and anti-communists.