Secretariat (March 30, 1970 – October 4, 1989), also known as Big Red, was a champion American thoroughbred racehorse who is the ninth winner of the American Triple Crown, setting and still holding the fastest time record in all three races. He is regarded as one of the greatest racehorses of all time. He became the first Triple Crown winner in 25 years and his record-breaking victory in the Belmont Stakes, which he won by 31 lengths, is widely regarded as one of the greatest races in history. During his racing career, he won five Eclipse Awards, including Horse of the Year honors at ages two and three. He was nominated to the National Museum of Racing and Hall of Fame in 1974. In the Blood-Horse magazine List of the Top 100 U.S. Racehorses of the 20th Century, Secretariat was second to Man o' War, although one of the seven voters left Secretariat out of their top 10.

At age two, Secretariat finished fourth in his 1972 debut in a maiden race, but then won seven of his remaining eight starts, including five stakes victories. His only loss during this period was in the Champagne Stakes, where he finished first but was disqualified to second for interference. He received the Eclipse Award for champion two-year-old colt, and also was the 1972 Horse of the Year, a rare honor for a horse so young.

At age three, Secretariat not only won the Triple Crown, but he also set speed records in all three races. His time in the Kentucky Derby still stands as the Churchill Downs track record for 1+1⁄4 miles, and his time in the Belmont Stakes stands as the American record for 1+1⁄2 miles on the dirt. His controversial time in the Preakness Stakes was eventually recognized as a stakes record in 2012. Secretariat's win in the Gotham Stakes tied the track record for 1 mile, he set a world record in the Marlboro Cup at 1+1⁄8 miles and further proved his versatility by winning two major stakes races on turf. He lost three times that year: in the Wood Memorial, Whitney, and Woodward Stakes, but the brilliance of his nine wins made him an American icon. He won his second Horse of the Year title, plus Eclipse Awards for champion three-year-old colt and champion turf horse.

At the beginning of his three-year-old year, Secretariat was syndicated for a record-breaking $6.08 million (equivalent to $37.1 million in 2021), on the condition that he be retired from racing by the end of the year. Although he sired several successful racehorses, he ultimately was most influential through his daughters' offspring, becoming the leading broodmare sire in North America in 1992. His daughters produced several notable sires, including Storm Cat, A.P. Indy, Gone West, Dehere and Chief's Crown, and through them Secretariat appears in the pedigree of many modern champions. Secretariat died in 1989 due to laminitis at age 19.