Gregory Sylvester Mangin (November 1, 1907 – October 27, 1979) was an American tennis player and Wall Street broker.

[5] Mangin won the Eastern Clay Court Championships in 1928 defeating Herbert Bowman in the final.

Mangin won the singles title at the U.S. Indoor Championships, held at the Seventh Regiment Armory in New York, in 1932, 1933, 1935 and 1936.

[6][7] In 1931, Mangin and Berkeley Bell were runners-up in the doubles final of the U.S. National Championships in Brookline, Mass., losing in straight sets to compatriots John Van Ryn and Wilmer Allison.

[8] During WWII Mangin enlisted in the United States Army Air Forces (AAF).