"Eclipse first and the rest nowhere," Capt. Denis O'Kelly remarked in 1769 as the colt, named for the year of the eclipse in which he was born, outstripped the rest of the pack by 240 yards.
Unbeaten in all 18 of his matches, Eclipse not only dominated the racing world in his time, but continues to influence the Thoroughbred world today. According to the Royal Veterinary Society, 80 percent to 90 percent of registered Thoroughbreds today can trace their lineage directly back to Eclipse. It is this careful recording of parentage that is one of the defining features in the establishing the Thoroughbred as a breed and as a sport horse.
The birth of the Thoroughbred is generally associated with three founding stallions and their direct offspring-Byerley Turk: King Herod (1689), The Godolphin: Matchen (1703), The Darley Arabian: Eclipse (1724). These Arabian horses were brought to England to lighten up the stock and bring endurance to some of the heavier horses.
The original Thoroughbreds were shorter, around 15.2 hands, and were better suited for the longer distances, much like their immediate ancestors. The English racing world, so enamored with the new breed, called for a posthumous dissection of Eclipse, revealing an unusually large heart, lungs and a powerful hind end.
Thoroughbred racing spread like wildfire, making its way to America in the years following the Revolution. It came in the form of a thought to be somewhat sterile, broken stud, Diomed. Adjusting well to his Bowling Green, Va., home, Diomed sprang to life and is credited with not only establishing the American TB, but also the Tennessee Walking Horse as well. To secure the authenticity of the TB as a breed, individuals kept careful breeding records until 1873, when Col. Sanders Bruce established the American Studbook.
It is the association with racing that defines this breed, although Thoroughbreds excel in many different areas of the horse world. Even the least horse-minded individual knows what a Thoroughbred is and can most likely name off Man O' War, Seabiscuit, or, more recently, Secretariat.

In the years preceding the Civil War, the famous American Eclipse stabled in the north was pitted against the southern bred Sir Archie and numerous other southern contenders to illuminate the already growing division of America. During the Great Depression, people found heroes in Thoroughbreds and found solace in the admirable spirit of the breed when brought against its opponents.
As the world changed, so did the Thoroughbred. Interest in short sprints, with an emphasis on speed rather than endurance, has created what we now recognize as a TB. The modern day TB is slightly leggier, standing around 16 hands and running up to 45 mph.
While this type of speed generally comes with a high-strung nature, all TBs cannot be considered a bundle of nerves. Rather, they are a sensitive and intelligent breed that tends to be very willing. Thoroughbreds mature young, generally racing as 2- and 3-year-olds and retiring at the early age of 5.
A great deal of credit should be given to this breed, as many thoroughbreds not only have a successful racing career, but they also manage to relearn everything that has been impressed on their green minds as a race horse to transition into the sport world. As a whole, this breed tends to bond to their person, learn quickly, and approach situations with heart and bravery.
Many TBs go on to have very successful Eventing or Hunter/Jumper careers. Their light build has long been desirable in crosses to create a sport horse with endurance and agility. Notwithstanding their versatility within the equestrian world, the Thoroughbred's true acclaim lies in its ability to transcend the horse world, as a player in televised mainstream sports.