American Classics/Breeders' Cup wins: Preakness Stakes (2007, 2009) Breeders' Cup Classic (2007)

Steven Mark Asmussen (born November 18, 1965, in Gettysburg, South Dakota) is an American Thoroughbred racehorse trainer. Born into a horse racing family, his parents, Keith and Marilyn "Sis" Asmussen, are both trainers who run El Primero Training Center off the Mines Road in western Laredo, the seat of Webb County in south Texas. His older brother, Cash Asmussen, is a retired Eclipse Award-winning jockey and a champion in Europe.

Asmussen began racing at age sixteen as a jockey, competing at racetracks in New Mexico, California, and New York for three years until his height and weight ended his riding career. In 1986 he began training Thoroughbreds and American Quarter Horses in New Mexico. In 2002, he led all trainers in Thoroughbred flat racing with 407 wins then in 2004 set a new record for wins by a trainer with 555, surpassing the mark of 496 held by Jack Van Berg since 1976.