Secretariat, also known as Big Red, was a champion American thoroughbred racehorse who was the ninth winner of the American Triple Crown, setting and still holding the fastest time record in all three of its constituent races. He is widely considered to be the greatest racehorse of all time. He became the first Triple Crown winner in 25 years and his record-breaking victory in the Belmont Stakes, which he won by 31 lengths, is often considered the greatest race ever run by a thoroughbred racehorse. During his racing career, he won five Eclipse Awards, including Horse of the Year honors at ages two and three. He was nominated to the National Museum of Racing and Hall of Fame in 1974. In the Blood-Horse magazine List of the Top 100 U.S. Racehorses of the 20th Century, Secretariat was second to Man o' 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.