Edward Geary Lansdale (February 6, 1908–February 23, 1987) was a US military officer who served in the Office of Strategic Services and the Central Intelligence Agency. He rose to the rank of Major General, was awarded the Distinguished Service Medal in 1963, and retired in 1968. Lansdale was born in Detroit, Michigan, died in McLean, Virginia, and is buried in Arlington National Cemetery.

After working to suppress Communist insurgency in the Philippines during the early 1950s, Lansdale took on his best-known role as a shaper of US strategy in Vietnam during the buildup to the Vietnam War. He was sent to Vietnam in 1953 as an advisor to French forces against the Viet Minh, and from 1954 to 1957 was stationed in Saigon as an advisor to the US-backed government of South Vietnam. During this period he was active in training the ARVN, organizing Caodaist militias under Trinh Minh The in an attempt to bolster the ARVN, and spreading claims that North Vietnamese agents were making attacks in South Vietnam. After the widely discredited re-election of Ngo Dinh Diem in 1955, Lansdale is said to have advised Diem to revise the 98.2 percent victory he claimed down to 70 percent to make it more plausible, advice which Diem did not take.

From 1957 to 1963 Lansdale worked for the Department of Defense in Washington, serving as Deputy Assistant Secretary for Special Operations, Staff Member of the President's Committee on Military Assistance, and Assistant Secretary of Defence for Special Operations. During the early 1960s he was chiefly involved in clandestine efforts to topple the government of Cuba, including proposals to assassinate Fidel Castro. According to Daniel Ellsberg, who was at one time a subordinate to Lansdale, Lansdale claimed that he was fired by President Kennedy's Defense Secretary Robert McNamara after he declined Kennedy's offer to play a role in overthrow of the Diem regime. Three weeks later, on November 22, 1963, Lansdale was photographed (from behind) in Dealey Plaza, Dallas, Texas, shortly after Kennedy was assassinated there. From 1965 to 1968 he returned to Vietnam to work in the US Embassy.

Lansdale's memoir, published in 1972, was In the Midst of Wars. His biography, The Unquiet American, was written by Cecil Currey and published in 1988; the title refers to the common belief that the eponymous character in Graham Greene's novel The Quiet American was based on Lansdale. Recent interest in Lansdale was sparked, in part, by Oliver Stone alleging in his 1991 film JFK that Lansdale was the operational head of the assassination of President John F. Kennedy on November 22, 1963. This theory was inspired by questions raised about Lansdale's presence in Dealey Plaza by a former employee of Lansdale, L. Fletcher Prouty, who first recognized Lansdale in a photograph taken that day by a Dallas Morning News photographer immediately after the assassination, which allegedly shows Lansdale, from behind, walking past "the three tramps " in Dealy plaza. That the photograph actually shows Lansdale has been corroborated by one of Lansdale's colleagues in the Pentagon, Lt. General Victor H. "Brute" Krulak . Ellsberg claims to have told Stone not to include this part of the script, believing Lansdale to be innocent of the conspiracy theory alleged by Stone.