American boxer who was the world heavyweight champion from July 3, 1905, to February 23, 1906. Hart's claim to the championship has not been universally accepted, although that of Tommy Burns (Burns, Tommy), who defeated Hart in a title match, is not seriously challenged.

After James Jackson Jeffries (Jeffries, James Jackson)—undefeated and lacking suitable opponents—resigned the championship in 1904, he arranged a fight to determine his successor. In this bout Hart knocked out Jack Root, a former 175-pound champion. Hart's only defense of the championship resulted in a 20-round decision in favour of Burns in Los Angeles. From 1899 to 1910, Hart had 48 bouts, of which he won 29, 20 by knockouts.