Conversation so far:
When was Man o'War born?
Man o' War's date of birth is March 29, 1917
Who was Man o' War's owner?
Man o' War's was Samuel Riddle
How many races did Man o' War run?
During his racing career just after World War I, Man o' War won 20 of 21 races
What kind of horse is Man o' War?
Man o' War was an American Thoroughbred who is widely considered one of the greatest racehorses of all time.
Did Man o' War have famous parents?
Man o' War was sired by Fair Play, a multiple stakes winner who finished second in the 1908 Belmont Stakes to the undefeated Colin.
What is interesting about Man o' War's background?
after the colt was foaled, Belmont Jr. joined the United States Army. While he was overseas, his wife named the foal Man o' War in honor of her husband.

Question: What was it most famous for?
Self-contained rewrite: What was Man o' War most famous for?