Diophon (1921 – after 1935) was a British Thoroughbred racehorse and sire. He was probably the best two-year-old colt of his generation in England in 1923 when he won four of his five races including the July Stakes Lavant Stakes and Middle Park Stakes. In the following spring he gave his owner Aga Khan III the first of his many classic wins when he took the 2000 Guineas. He failed to win again that year but returned to take three valuable prizes in 1925. After his retirement from racing he had some success as a breeding stallion.