Simplify the following text for a Grade 9 native English-speaking person.
Original: Rocky Marciano ( September 1 , 1923 â `` August 31 , 1969 ) , born Rocco Francis Marchegiano , was an Italian-American boxer and the heavyweight champion of the world from September 23 , 1952 , to April 27 , 1956 .
Simplified: Rocco Francis Marchegiano , better known as Rocky Marciano ( September 1 , 1923 â `` August 31 , 1969 ) , was an American boxer . Marciano was the World Heavyweight Boxing Champion from 1952 until 1956 .