Isonomy was a bay colt by Sterling, out of Isola Bella, by Stockwell, foaled in 1875. He was one of the most popular and durable performers of his era, and an influential stallion who produced two English Triple Crown winners and two outstanding sire sons. He was bought at the Doncaster sales by the trainer John Porter for one of his owners Frederick Gretton for 360 guineas. Porter trained Isonomy at his Kingsclere yard. As a juvenile, Isonomy started only three times, and finished the season with a win, a place and a third. His next race was not until October the following season in 1878 when he won the Cambridgeshire Handicap by two lengths. At four, Isonomy was out eight times, and won six races including the Ascot Gold Cup, Goodwood Cup, the Brighton Cup and the Great Ebor Handicap at York which he won by eight lengths. His final win was the Doncaster Cup ridden by Tom Cannon. It would be another seventy years before another horse won the English Triple Crown. As a five-year-old, he won the Manchester Cup and the Ascot Gold Cup. He was then sent to stud and produced many winners including Isobar, Common and Isinglass.