Gregory S. Mangin (November 1, 1907 - October 1979) was an American former tennis player.
Mangin was educated at the Georgetown University and learnt lawn tennis in Montclair, New Jersey.
In 1931 Mangin, partnering compatriot Berkeley Bell, were runners-up in the doubles final of the U.S. National Championships, played in Brookline, MA, losing in straight sets to compatriots John Van Ryn and Wilmer Allison.
He won the singles title at the U.S. Indoor Championships, played at the Seventh Regiment Armory in New York, in 1932, 1933, 1935 and 1936.
He was a member of the US Davis Cup teams in 1930 and 1931 but did not play any matches.
During WWII Mangin enlisted in the United States Army Air Forces (AAF). He became a tail gunner on the B-17 Flying Fortress and flew 50 missions over Europe. He was wounded twice in missions over Italy and France and shot down two ME-109s in a mission over Germany. Reaching the rank of staff sergeant he received the Distinguished Flying Cross (DFC), the Air Medal with six clusters and a Purple Heart with one cluster.