Jackson, Reggie (Reginald Martinez Jackson), 1946–, American baseball player, b. Wyncote, Pa. In 21 years in the American League, most notably with the Oakland Athletics and New York Yankees, he hit 563 home runs, winning or sharing four home run titles, and struck out a record 2,597 times. An outspoken player who starred in clutch situations, he became known as Mr. October, especially after his performance in the 1977 World Series, when he hit five home runs, three in the deciding game.