American professional baseball manager and team executive, the “grand old man” of the major leagues in the first half of the 20th century. He managed the Philadelphia Athletics (A's) from 1901 through 1950, during which time they won nine American League championships and five World Series (1910–11, 1913, 1929–30). He was president of the club from 1937 through 1953.

Mack played, chiefly as a catcher, in about 700 major league games with Washington (1886–89), Buffalo (1890), and Pittsburgh (1891–96). While a player, he shortened his name so that it would fit on a scoreboard. Mack also managed Pittsburgh from September 3, 1894, through the 1896 season.

In 1897 Mack joined the Milwaukee club in the Western League (renamed the American League in 1900) as playing manager. In 1901 he became manager and part owner of the Philadelphia A's and helped establish the American League as a major league. In his 53 years of managing in the big leagues, his teams won 3,776 games and lost 4,025, both all-time records. In 1937 he was elected to the Baseball Hall of Fame in Cooperstown, New York.