Sonny Corleone (James Caan)’s Timeline and Summary

When we first see him, Sonny's sneaking away to cheat on his wife at his sister's wedding. He also intimidates FBI men who are writing down license plate numbers and smashes a photographer's camera.
After the assassination attempt on his father fails, Sonny orders a (successful) hit on the Tattaglia Don's son, Bruno. But he makes the decision out of anger, not strategy, further inflaming tensions.
When his sister's husband, Carlo, beats her, Sonny publicly attacks Carlo in the street, hitting him over and over again.
Carlo attacks her again, this time to force Sonny to leave the family's compound. When Sonny races out in a car to punish Carlo again, he's ambushed at a tollbooth and assassinated in an extremely bloody fashion.