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 operate El Primero Training Center off the Mines Road in Laredo, the seat of Webb County in south Texas. His older brother, Cash Asmussen, currently a trainer himself, is a retired Eclipse Award-winning jockey and a champion in Europe.