Donald Stetson Mason (December 20, 1944 – June 19, 2018) was an American professional baseball player. The second baseman appeared in 336 games in Major League Baseball over all or parts of eight seasons (1966–1973) for the San Francisco Giants and San Diego Padres. Mason also played three other full seasons in the National League (1969, 1970 and 1971), exceeding 100 games played in 1969 and 1971. In the latter year, he was the most-used second baseman for the 1971 Padres, starting 90 games at the position, but Mason batted only .212 will 11 runs batted in.