Standardbreds are so named because in the early years of the Standardbred stud book, only horses who could trot or pace a mile in a standard time (or whose progeny could do so) of no more than 2 minutes, 30 seconds were admitted to the book. Today, most harness races are won by Standardbreds who post times of 2 minutes or less. The horses have proportionally shorter legs than Thoroughbreds, and longer bodies. Standardbreds generally have a more placid disposition, due to the admixture of non-Thoroughbred blood in the breed.

The founding sire of today’s Standardbred horse was Messenger, a gray Thoroughbred brought to America in 1788 and purchased by Henry Astor, brother of John Jacob Astor.

From Messenger came a great-grandson, Hambletonian 10 (1849–1876), who gained a wide following for his racing prowess.
However, it is his breed line for which he is most remembered. The lineage of virtually all North American Standardbred race horses can be traced from four of Hambletonian 10 sons