Question: who is the only professional boxer to end his career undefeated with a record of 49-0
Answer: Rocco Francis Marchegiano ( September 1 , 1923 -- August 31 , 1969 ) , best known as Rocky Marciano ( / mɑːrsiˈɑːnoʊ / ) , was an American professional boxer who competed from 1947 to 1955 .