Simplify the following text for a Grade 6 native English-speaking person.
Original: Sugar Ray Robinson ( born Walker Smith Jr. , May 3 , 1921 â `` April 12 , 1989 ) was an American boxer who won the welterweight and middleweight world championships .
Simplified: Sugar Ray Robinson ( born Walker Smith Jr. , May 3 , 1921 â `` April 12 , 1989 ) was a professional boxer .