William Stuart Symington III (June 26, 1901 – December 14, 1988) was an American businessman and Democratic politician from Missouri. He served as the first secretary of the Air Force from 1947 to 1950 and was a United States senator from Missouri from 1953 to 1976.

Born in Amherst, Massachusetts, Symington worked as an executive in his uncle's iron products company and for other companies before becoming president of Emerson Electric. He resigned from Emerson in 1945 to take various positions in the administration of President Harry S. Truman, becoming the first Secretary of the Air Force in 1947. He was elected to the Senate in 1952, defeating incumbent Republican Senator James P. Kem. He joined the United States Senate Armed Services Committee and the United States Senate Committee on Foreign Relations, and emerged as a prominent critic of McCarthyism.