Tranquil Star (foaled in 1937) was one of the hardiest and best performed Australian-bred Thoroughbred race-mares. She is the only mare to have won the double of the Caulfield Stakes, now known as the Yalumba Stakes, and the Cox Plate, which is the most prestigious weight-for-age (wfa) race in Australia. Tranquil Star had 111 starts and won over distances ranging from 5 furlongs (1,000 metres) to 14 furlongs (2,800 metres). She was later inducted into the Australian Racing Hall of Fame.