William John Hartack Jr., born December 9, 1932 in Ebensburg, Pennsylvania, United States, is a Hall of Fame jockey.

Bill Hartack grew up on his widowed father's farm in the Blacklick Township area of Cambria County, Pennsylvania. Small in stature, at age 17 he stood 5'4" and weighed 111 lbs, a size that enabled him to pursue a career as a jockey in thoroughbred horse racing. By his third season of racing, Hartack was the United States' leading jockey, going on to win that honor on three more occasions. He and Eddie Arcaro (1916-1997), are the only two jockeys to ever win the Kentucky Derby five times. As well, Hartack won the Preakness Stakes three times and the Belmont Stakes once. Two weeks before the 1958 Kentucky Derby he broke a leg and had to give up his ride on Tim Tam who won the race. During his riding career between 1953 and 1974 in the United States, Hartack rode 4,272 winners in 21,535 mounts. From 1978 to 1980 he raced in Hong Kong, then retired in 1981.

Referred to by the media for several years as "Willie" until he advised them he was actually known as "Bill," Hartack made the cover of Sports Illustrated magazine in 1956 and again in 1964, plus the cover of Time Magazine in 1958. He was inducted into the National Museum of Racing and Hall of Fame in 1959.

Winners ridden in Triple Crown races :