William "Sonny" Brewster Van Arsdale IV (later Corleone) was the only son and second child of William Van Arsdale III and Francesca Corleone. He was the younger brother of Carmela Van Arsdale. He was affectionately nicknamed "Sonny" after his maternal grandfather, Sonny Corleone.

After the death of his father, he lived with his mother, Francesca, and adopted the use of her maiden name, Corleone.

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