Gabriel Marie "Gai" Waterhouse is an Australian horse trainer and businesswoman. The daughter of Tommy J. Smith, a leading trainer of Thoroughbred racehorses, Waterhouse was born and raised in Sydney. After graduating from the University of New South Wales, she worked as an actor for a time, appearing in both Australian and English television series. Having worked under her father for a period of 15 years, Waterhouse was granted an Australian Jockey Club (AJC) licence in 1992, and trained her first Group One (G1) winner later that year.

Thomas John Smith was a leading trainer of thoroughbred racehorses based in Sydney, New South Wales.