Diomed (1777–1808) was an English Thoroughbred race horse who won the inaugural running of the Epsom Derby in 1780. Sold and imported to Virginia, he was subsequently a successful sire in the United States after the American Revolutionary War.

The Thoroughbred is a horse breed developed for horse racing. Although the word thoroughbred is sometimes used to refer to any breed of purebred horse, it technically refers only to the Thoroughbred breed. Thoroughbreds are considered "hot-blooded" horses that are known for their agility, speed, and spirit.