Question: Which Racehorse was the daughter of the American Thoroughbred was the unofficial 1920 American Horse of the Year, considered one of the greatest racehorses of all time?
Sentence (from "Man o' War"): Man o' War (March 29, 1917 – November 1, 1947) was an American Thoroughbred who is widely considered one of the greatest racehorses of all time.
Relevant evidence: Yes