Bay Middleton was an undefeated Thoroughbred racehorse whose victories included two British Classic Races. He was twice the Leading sire in Great Britain and Ireland.

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.