One of the most influential stallions of all time, St. Simon was bred in England by Prince Batthyany of Hungary. The Prince owned both Galopin and St. Angela, his sire and dam. Upon the death of the Prince, his horses were sold. Galopin went to Mr. Henry Chaplin for 8,000 guineas, and St. Angela, in foal to Galopin, went to Leopold de Rothschild for 320 guineas and was sent to France. Trainer Matthew Dawson purchased St. Simon for the Duke of Portland for 1,600 guineas.
Standing 16.1 hands, many considered St. Simon to have flawless conformation, however, he was noted for his highly strung temperment. He was unbeaten as a racehorse, his ten victories spanning five furlongs to two miles and five furlongs, with none causing him to really extend himself. He won the Ascot Gold Cup (2 1-2 miles) by twenty lengths, with so much left he went another mile before he would consent to being pulled up. He retired to stud at four years of age, completely sound, first at Matthew Dawsons Heath Farm, and later at the Dukes Welbeck Stud.
At stud he was Champion Sire nine times and Champion Broodmare Sire six times. The number of his offspring successful at racing or stud was enormous, and includes Derby winners Persimmon and Diamond Jubilee, both from Perdita 2nd , and Oaks winners La Fleche and her full sister Memoir, Mrs. Butterwick, Amiable, and La Roche. Other influential offspring include St. Frusquin, St. Serf, Florizel 2nd , Chaucer, Desmond, William The Third and Rabelais.
Another son, St. Florian (br.c. 1891) did not make much of mark on the racecourse, although he did win the Duke of York Stakes. St. Florian sired Ard Patrick (br.c. 1899) who was sent to Germany where he in turn sired Ariel (b.c. 1911), and Slieve Gallion (bl.c. 1904) who was sent to Hungary. He was among the Champion Broodmare Sires five times.
St. Simon died at Welbeck in 1908