Man o' War was an American Thoroughbred racehorse who is widely regarded as one of the greatest racehorses of all time. Several sports publications, including The Blood-Horse, Sports Illustrated, and the Associated Press, voted Man o' War as the best American racehorse of the 20th century. During his racing career, just after World War I, Man o' War won 20 of 21 races and $249,465 in purses. He was the unofficial 1920 American horse of the year and was honored with Babe Ruth as the outstanding athlete of the year by The New York Times. He was inducted into the National Museum of Racing and Hall of Fame in 1957. On March 29, 2017, the museum opened a special exhibit in his honor, "Man o' War at 100".

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.