The Byerley Turk, also spelled Byerly Turk, was the earliest of three stallions that were the founders of the modern Thoroughbred horse racing bloodstock.

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.