In the film, Sonny was portrayed by James Caan, who briefly reprised his role for a flashback scene in The Godfather Part II.

Sonny replies that he had witnessed Vito murder the "Black Hand" gangster Don Fanucci years before, and he now wants to join the "family business".

By the end of World War II, he is his father's underboss and heir apparent, popular and feared as a merciless killer with a short temper.

Sonny is not without a sensitive side, however; at age 11, he brings home a homeless boy, Tom Hagen, demanding he be allowed to live with the family.

Sonny's life is upturned in 1945, when drug lord Virgil "The Turk" Sollozzo, backed by the Tattaglia family, approaches Vito with an offer to enter the narcotics trade.

Sollozzo later attempts to have Vito assassinated, believing Sonny, as his father's successor, will bring the Corleone family into the drug trade.

The failed assassination attempt leaves Vito near death, making Sonny acting boss of the Corleone family.

Sonny is impressed with Michael's confidence and seriousness, but doubts that his "nice college boy" brother is capable of murder.

The war between the Five Families drags on, and Sonny, unable to break the stalemate, orders bloody raids that earn him a legendary reputation.

Emilio Barzini, Vito's rival and the power behind Sollozzo, enlists Connie's abusive husband, Carlo Rizzi, to help set a trap.

During a meeting with the other crime family dons to establish peace, Vito realizes that Barzini masterminded Sonny's murder.

After Vito dies in 1955 from a heart attack, Michael has the other dons murdered, including Barzini, who is shot twice in the back on the steps of a courthouse in broad daylight.

Vincent's existence in the film contradicts Puzo's original novel, which stated that Lucy never bore a child with Sonny.