William David Parker (January 14, 1942 – February 9, 2003) was a professional baseball player who played parts of three seasons for the California Angels of Major League Baseball. He is the first player to hit a walk-off homer in his major league debut, doing so on September 9, 1971 for the Angels. Parker's professional baseball career began in 1961 with the Negro league Indianapolis Clowns, where he played through 1964.