Rocky Marciano (1923-1969) was the only heavyweight champion ever to complete a professional career without a loss. Rocky's record was 49-0, with 43 KOs. He was the greatest slugger in boxing history and knocked out 88 percent of his opponents. Born Rocco Marchegiano, he grew up during America's Great Depression and by 1947 he was the darling of the New York fight crowd. Later that year he turned professional and he became the heavyweight champion of the world when he defeated Jersey Joe Walcott on September 23, 1952. He defended his title six times and retired undefeated in 1956.