Mill Reef (23 February 1968–2 February 1986) was an American-bred, British-trained Thoroughbred racehorse and sire. In a three-year career from 1970 to 1972, he won twelve of fourteen races and finished second in the other two. The horse was an outstanding two-year-old in 1970 but proved even better at three, winning the Epsom Derby, the Eclipse Stakes, the King George VI and Queen Elizabeth Stakes and the Prix de l'Arc de Triomphe. He won both his starts as a four-year-old before his racing career was ended by injury. Mill Reef is considered one of the greatest horses to run in Europe since WWII.