John Gregory Bourke (June 23, 1843 – June 8, 1896) was a captain in the United States Army and a prolific diarist and postbellum author; he wrote several books about the American Old West, including ethnologies of its indigenous peoples. He was awarded the Medal of Honor for his actions while a cavalryman in the Union Army during the American Civil War. Based on his service during the war, his commander nominated him to West Point, where he graduated in 1869, leading to service as an Army officer until 1886.