 Sometimes called the "Giant Killer", he is best known for his upsets.Jerkens saddled the 1973 Whitney Handicap winner Onion (defeating Secretariat), 1973 Woodward Stakes and Jockey Club Gold Cup winner Prove Out (defeating Secretariat and Riva Ridge, respectively), and Beau Purple, who defeated Kelso in three of their four meetings.His horses defeated other greats such as Buckpasser, Cougar II, and Forego.