William John "Wild Bill" Hapac (January 26, 1918 – March 9, 1967) was the first consensus All-American to play for the University of Illinois men's basketball team when he garnered the recognition during his senior season of 1939–40.

He set a then-unheard of Big Ten Conference single game scoring record of 34 points against Minnesota on February 10, 1940.

Hapac finished his professional career by playing for an independent league team, the Chicago Ingots, for the 1947–48 season.

[1] Hapac was pursued by the Detroit Tigers, but while waiting for spring training to begin, he was inducted into the US Army, eventually earning him the rank of captain.

Hapac coached basketball with fellow Illini player, Jim Vopicka, at Morton East from 1952 until his death in 1967 at 49 years of age of an undisclosed rare disease.