William A. Foster (September 18, 1937 – January 20, 1967), was a Canadian racing driver.
Born in Victoria, British Columbia, Foster died in a crash during practice for a NASCAR stock car race at Riverside International Raceway in Riverside, California. Foster is the only Canadian racing driver to have been fatally injured at a NASCAR event. He is also one of the only three non American drivers (Mexicans Marcelo Núñez and Carlos Pardo are the other) to be fatally injured at a NASCAR event. He also drove in the USAC Championship Car series, racing in the 1964-1966 seasons, with 28 career starts, including the 1965 and 1966 Indianapolis 500 races. He finished in the top ten 10 times, with his best finish in 2nd position in 1966 at Atlanta.
He and Mario Andretti became best of friends, building a close relationship which Andretti claimed he would never do again with a fellow racer because Foster's death so significantly affected him.
Foster was cousins with musician, producer, composer, arranger David Foster and with Canadian stock car driver Jim Steen.
He was inducted into the Canadian Motorsport Hall of Fame in 1993.