Lord Lyon (1863–1887) was a British Thoroughbred racehorse that won the 1866 Epsom Derby, 2,000 Guineas Stakes and the St. Leger Stakes, becoming the third winner of the English Triple Crown. Lord Lyon raced until he was four-years old and was retired to stud in 1868. He is considered to be a marginally successful sire with his most notable progeny being the colt Minting and the filly Placida. He was euthanized in April 1887 after several years of failing health.

The Derby Stakes, also known as the Derby or the Epsom Derby, is a Group 1 flat horse race in England open to three-year-old colts and fillies. It is run at Epsom Downs Racecourse in Surrey on the first Saturday of June each year, over a distance of one mile, four furlongs and 10 yards, or about 1½ miles. It was first run in 1780.