The Godfather

In the mid-1940s, 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 of his family but makes it clear that he wants no part in his family's business.

Vito fulfils the Sicilian tradition of granting favors on his daughter's wedding day to a succession of hopeful visitors. One is his godson, singer and actor Johnny Fontane, who cannot get an upcoming film role because studio owner and producer Jack Woltz has a grudge against Fontane. Vito sends Hagen to LA to persuade Woltz to relent but Woltz will not budge. Hagen departs and the next morning, Woltz wakes to find the severed head of his prized $600,000 racehorse Khartoum in his bed with him. A terrified Woltz relents and Fontane gets the role.

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, hot-tempered Sonny takes over the family as acting boss. He has Michael live at the house for his protection, as his successful revenge hit on Tattaglia's son Bruno has led to war between the two gangs. Michael visits his father in hospital to be told that NYPD Captain McCluskey has had Vito's bodyguards ejected from the hospital, clearing the way for a second attempt on Vito's life. Michael visits his father and, realizing his jeopardy, moves him to another hospital room then stands guard outside the hospital. He scares Sollozzo's assassins off but an angry McCluskey returns and breaks Michael's jaw for defying him. Soon after, Hagen arrives with more bodyguards and McCluskey backs down to the lawyer's demands. Being an outsider to the family business and seen as harmless, Michael later proposes a meeting between himself, Sollozzo and McCluskey at which he'll kill them both to keep his father safe. Initially amused, the family approve his plan and have 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 until the heat dies down. 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 discovers that Connie was being abused by Carlo. At first, Sonny pummels Carlo in public and warns him never to touch Connie again. However, after a fierce beating from Carlo, Connie appeals to her family. A furious Sonny sets off for her house but is ambushed and murdered at a highway toll booth. The recovering Vito is told of Sonny's death and orders an end to hostilities with no vengeance. He calls a meeting with the heads of the other New York families and negotiates peace between them all, conceding to a controlled drug trade in return 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 via car bombing. He returns to the US, slowly taking over the family business from his father. He marries Kay and promises to legitimize the family's operations within five years.

Michael visits Las Vegas to negotiate a deal with Jewish mobster and casino mogul 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 and warns him never to side against the Family ever again.

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 will reveal himself by offering to broker a meeting between Michael and the Barzinis but will use it to have Michael assassinated. 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 lure Sonny into his fatal ambush. Michael berates Carlo, then sends him on an apparently safe car journey where instead 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. Kay watches Clemenza kiss Michael's hand and address him as "Don Corleone" before Neri closes the door on her.