In May 1886 The Sporting Times' carried out a poll of one hundred experts to create a ranking of the best British racehorses of the 19th century.

[1] St. Simon was bred by Prince Gustavus Batthyany of Hungary and foaled at William Barrow's Paddocks near Newmarket.

Her other notable progeny was a full-sister to St. Simon named Angelica, who later became the dam of champion and major stallion Orme (1889 by Ormonde).

Reportedly Batthyany's trainer John Dawson had painted the colt's hocks with a suspicious white substance, perhaps in an effort to discourage bidders.

[3] The colt began his racing career under jockey Fred Archer at the five furlong Halnaker Stakes at Goodwood, winning by six lengths.

He then easily won a five-furlong race against Clochette and Fleta, the five-furlong Devonshire Nursery Plate (against 19 other horses), carrying 8 stone 12 pounds (124 lb) by two lengths at a canter, and the seven-furlong Princes of Wales's Nursery Plate (Doncaster) carrying 9 stone (130 lb; 57 kg) and winning by eight lengths against 21 other horses.

He then won the 2½ mile Ascot Gold Cup by 20 lengths, despite having trailed in the beginning of the race, to beat Tristan and Faugh-a-Ballagh.

[4] In the one-mile Newcastle Gold Cup, he beat his only other competitor, Chiselhurst, by eight lengths, but suffered some damage due to the hard ground.

St. Simon retired to stud in 1886 and sired 423 live foals, who between them won 571 races and more than half a million pounds in stake-money from 1889 through the first decade of the twentieth century.

[14] Nearco's grandson Northern Dancer, another enormously influential sire, has fifteen crosses to St. Simon in the first eight generations of his pedigree.

[15] Pedigree expert Anne Peters refers to his bloodline as "one of the most widespread and omnipresent in the Thoroughbred gene pool today.