When the 151st Kentucky Derby is set to be run on May 3 at Churchill Downs in Louisville, Kentucky, it marks the first leg of the American Thoroughbred Triple Crown, the crown jewel of horse racing.

A horse who emerges victorious in the Kentucky Derby, Preakness Stakes and Belmont Stakes is dubbed a Triple Crown winner. The Belmont Stakes typically is the longest race at 1 1/2 miles.

The Triple Crown is an accomplishment that a select group of horses has achieved throughout history. When a horse wins all "jewel" races in a single season -- the Kentucky Derby, Preakness Stakes ...