Marciano, Rocky (1923-1969), American boxer, who retired as the only undefeated heavyweight champion in boxing history. Born Rocco Francis Marchegiano in Brockton, Massachusetts, he began boxing in the United States Army in 1943 and continued fighting under an assumed name, Rocky Mack, to preserve his amateur status. Marciano turned professional in 1947, and in 1951 he wept after knocking out his boyhood hero, former world champion Joe Louis.
In September 1952, Marciano knocked out Jersey Joe Walcott to win the heavyweight championship in one of his most memorable fights. Trailing on the judges' scorecards at the time of the knockout, Marciano displayed his power, tenacity, and will to win when he scored the 13th-round knockout. He successfully defended his title six times between 1953 and 1955. By the time he retired in April 1956, he had a record of 49-0, with 43 wins by knockout. Marciano died in a light plane crash in 1969.