William Hendrick Foster was an American left-handed pitcher in baseball's Negro leagues in the 1920s and 1930s, and had a career record of 110–56. He was elected to the Baseball Hall of Fame in 1996. Foster was the much-younger half-brother of Rube Foster, a Negro league player, pioneer, and fellow Hall of Famer.

The Negro leagues were United States professional baseball leagues comprising teams of African Americans. The term may be used broadly to include professional black teams outside the leagues and it may be used narrowly for the seven relatively successful leagues beginning in 1920 that are sometimes termed "Negro Major Leagues".