John Shirreffs is a well-known American horse trainer, recognized for his success in thoroughbred racing. He has trained several notable racehorses, including Zenyatta, a champion mare who won numerous prestigious races and became a fan favorite. Shirreffs is known for his calm demeanor and ability to develop horses into top competitors. Shirreffs began his training career in the 1990s and has since built a reputation for his skill in preparing horses for major events. His training methods emphasize the importance of understanding each horse's unique needs and capabilities, which has contributed to his success in the racing industry.