Clarence Joseph Kummer (August 8, 1899 – December 18, 1930) was a U.S. Racing Hall of Fame jockey who won four American Classic Races.
In early 1920, Kummer rode the 1919 Triple Crown Champion Sir Barton to a new Saratoga track record in winning the Saratoga Handicap. In May 1920 he was given the opportunity to ride Man o' War. He rode the horse to nine wins in nine starts. Kummer's successes in 1920 made him that year's top money-winning jockey in the United States.
Clarence Kummer won the Preakness and Belmont Stakes twice each and had four mounts in the Kentucky Derby with his best result a second-place finish in 1923. In a relatively short career he won numerous important races, including the 1925 edition of the prestigious Travers Stakes, but by the end of the latter part of the 1920s constantly battled weight gains and was forced to retire after the 1928 racing season in which he had won his second Belmont Stakes.