The Godfather

Michael Corleone is a World War II veteran and the youngest son of Don Vito Corleone. Vito is head of the Corleone mafia family and runs it with his eldest son Santino a.k.a. Sonny and adopted son Tom Hagen, a lawyer who is the family's consigliere. At his sister Connie's wedding to Carlo Rizzi, Michael introduces his family to his girlfriend, Kay Adams. Michael tells Kay stories about his family, ending with his desire to have no part in his family's business.

Approaching Christmas, Michael becomes embroiled in family affairs when Vito is gunned down by two assailants. Vito had earlier refused to offer protection to drug baron Virgil "The Turk" Sollozzo for dealing narcotics in the city. Sollozzo has the support of the Tattaglia family, who garrote notorious Corleone enforcer Luca Brasi when he attempts to become a mole in Sollozzo's operation. While Vito survives the attempt and recovers at the hospital, Sonny takes over the family as acting boss. He has Michael live at the house for his protection, as a successful hit on Tattaglia's son Bruno leads to war between the two gangs. NYPD Captain McCluskey arrests Vito's bodyguards to allow Sollozzo to make another attempt on Vito's life, which is stopped by Michael and Enzo. Being an outsider to the family business and seen as harmless, Michael proposes a meeting between himself, Sollozzo, and McCluskey at which he'll kill them both to keep his father safe. Initially amused, the family approves his plan and has a gun planted at the meeting place: a restaurant. At the meeting, Michael shoots both men dead, then flees the country. He takes refuge in his family's native Sicily to escape the NYPD and the ire of the other gangs. He falls in love with a local woman, Apollonia Vitelli, and marries her.

Back in New York, war has broken out between the Five Families. Sonny receives a distress call from Connie, who is being abused by Carlo. En route to her house, he is ambushed and murdered at a highway toll booth. With Sonny dead and his middle son Fredo unfit to rule, the recovering Vito orders an end to hostilities. He negotiates peace with the other Family heads, offering a controlled drug trade and access to his political connections in exchange for an end to all vendettas and for Michael's safe return to the US. Meanwhile, Michael survives a hit in Sicily, which instead kills Apollonia. He returns to the US, slowly taking over the family business from his father. He marries Kay and promises to legitimize the Corleone family's operations within five years.

Michael visits Las Vegas to negotiate a deal with Jewish mobster Moe Greene, under whose protection Fredo has been living. Michael offers to buy out Greene's stake in the family casinos, but Greene refuses and flaunts his support from Barzini. After Moe leaves, Michael reprimands Fredo for defending Greene.

After the peace meeting, Vito realizes that Barzini is the mastermind behind Sonny's death, not Tattaglia. He predicts to Michael that a Corleone traitor might reveal himself by offering to broker a deal between Michael and the Barzinis that will really be for Michael's assassination. Vito dies of a heart attack while playing with his grandson, Michael's son Anthony. At his funeral, Corleone caporegime Salvatore Tessio asks Michael to meet with Barzini, revealing his betrayal. Michael attends his nephew's baptism to be anointed as his godfather while Michael's hitmen carry out orders, simultaneously assassinating Greene and the heads of the other New York Families. Tessio is led off to be executed for his treachery. Michael extracts a confession from Carlo that he conspired with Barzini to kill Sonny and had abused Connie to tempt Sonny into his fatal ambush. Michael berates Carlo, then tricks him into entering a car where Clemenza garrotes him.

At their house, Connie accuses Michael of having Carlo killed. To Kay's relief, Michael denies the accusation, but as she leaves the room to get drinks, the Corleone family capos approach Michael and offer him their allegiance. As Kay looks on with trepidation, Clemenza kisses Michael's hand and addresses him as "Don Corleone" while Neri closes the door on her.