By 1979, the activities of the Corleone family were nearly completely legitimate. Michael Corleone sold their interests in all casinos and hotels and invested only in businesses unconnected to Mafia activities. The underboss of the Corleone's criminal enterprise, Joey Zasa, resentful of the reforms, aligned with aging kingpin Don Altobello, and together orchestrated an assassination attempt on Michael Corleone during a meeting in Atlantic City.
While , in 1980, Michael appointed his nephew and Sonny's illegitimate son, Vincent Mancini, to be his successor as Don of the Corleone family, he allowed him to change his name to Vincent Corleone. In return for this, Michael ordered him to end his relationship with Michael's daughter (and Vincent's cousin) Mary Corleone. Vincent assured him that he would.
Under Michael's mentoring, Vincent is remade into a new man - wiser, patient, and aware of his status as the new Don. However, he retained a violent streak, as evidenced in his first act as Don. With Michael's tacit blessing, he ordered the deaths of Gilday, Keinszig, and Lucchesi in one mass slaughter. However, Mary was killed in a failed assassination attempt on Michael. Vincent quickly and ruthlessly killed Mosca, the assassin responsible. Despite this, Michael still dies alone and despondent after an unknown period of time.