Leroy Gordon "Gordo" Cooper Jr. was an American aerospace engineer, test pilot, United States Air Force pilot, and the youngest of the seven original astronauts in Project Mercury, the first human space program of the United States. Cooper learned to fly as a child, and after service in the United States Marine Corps during World War II, he was commissioned into the United States Air Force in 1949. After service as a fighter pilot, he qualified as a test pilot in 1956, and was selected as an astronaut in 1959.