Equipoise (1928–1938) was an American Thoroughbred racehorse and sire. In a career which lasted from 1930 until 1935, he ran fifty-one times and won twenty-nine races. A leading two-year-old in 1930, he missed most of the next season, including two of the three American Triple Crown races through injury and illness. "Ekky" returned to the track in 1934 and proved to be a dominant champion, winning numerous important stakes races in the next three years. Equipoise died in 1938 after a short but promising stud career.

Equipoise was a chestnut bred in the United States by Harry Payne Whitney and owned by his son, Cornelius Vanderbilt Whitney. He was called the "Chocolate Soldier" by his fans, due to his elegance and symmetry. His sire, Pennant, won the Belmont Futurity Stakes for Harry Payne Whitney in 1913. Equipoise's dam, Swinging, was a descendant of The Oaks winner Miami, placing him in the same Thoroughbred family as the 1897 English Triple Crown winner Galtee More and the 1902 Epsom Derby winner Ard Patrick as well as some well-known American runners, such as Intentionally and Seabiscuit.

As a yearling, Equipoise was an unimpressive individual. C. V. Whitney thought so little of the ugly duckling that he sent him to his second-string trainer, Fred Hopkins.

As a two-year-old, Equipoise ran sixteen times, claiming his first stakes victory when he won the Keene Memorial Stakes at Belmont Park. In September, he ran in the Belmont Futurity the most valuable two-year-old race of the season in which he was beaten a nose by Jamestown. Although Jamestown's victory was regarded by some as having decided the identity of the best two-year-old, he did not race again in 1930, while Equipoise went on to further success. On November 5, he beat Twenty Grand by half a length with Mate a neck away in third in the Pimlico Futurity. After starting slowly, he settled the race in the straight with what the New York Times described as "a brilliant burst of speed" to reverse two earlier defeats by Twenty Grand. When his jockey, Sonny Workman, was asked if this was his greatest race, Workman replied: "My greatest race? Hell, it may have been the greatest race anybody ever saw."

Although there were no formal awards for Thoroughbred racing in 1930, press opinion was that Equipoise's win at Pimlico entitled him to "a share of the 2 year old championship honors"

Equipoise started 1931 as the favorite for the Kentucky Derby and won on his reappearance at Havre de Grace, Maryland. At the same track on April 26, he finished last of the six runners in the Chesapeake Stakes, after which he was reported to be suffering from a kidney ailment described as "azoturia" or "blackwater". Later reports ascribed his defeat to problems with his "shelly" feet. In the Preakness Stakes, which was the first of the Triple Crown races in 1931, he finished fourth behind Mate. A week later, he was withdrawn from the Derby on the day of the race and did not race again that year.

As a four-year-old in 1932, Equipoise won ten of his fourteen starts. On May 21, he won the Metropolitan Handicap at Belmont Park from Sun Meadow, with Mate third. Equipoise, who started 3/5 favorite, won by two and a half lengths despite being eased down by Workman near the finish and was received with "thunderous applause". On May 31 at Arlington Park, Chicago, Equipoise set a world record of 1:34.4 for a mile when winning the Delavan Purse. In the Stars and Stripes Handicap at the same course four days later, he "outclassed" his opponents. On August 13, Equipoise led all the way to win the Whitney Stakes by three lengths from the three-year-old Gusto. According to the New York Times report, the win confirmed his status as the best horse in the handicap division.

At five, Equipoise won seven more races. On June 3, he gave 26 pounds to the runner-up, Okapi, in again winning the Metropolitan, living up to his reputation as the "king of the handicap horses". Four days later, he ran in the Suburban Handicap carrying 132 pounds over a mile and a quarter. He won by two lengths from Osculator, with Apprentice five lengths back in third. In August, he faced the highly regarded Gallant Sir in the Hawthorne Gold Cup and won a "thrilling" race by two lengths to record his sixth successive win. His other wins included April's Philadelphia Handicap at Havre de Grace Racetrack which he won again in 1934. In September he won the Saratoga Cup in which he raced beyond a mile and a quarter for the first time and won from Gusto and Keep Out.