I have watched Godfather at least 5 times.

it was acted by Marlon Brando, Al Pacino, Robert Duvall, Talia Shire.

here is Synopsis for Godfather from google:
The film begins at the wedding of Don Vito Corleone's daughter Connie to Carlo Rizzi in late summer of 1945, on Long Island, New York. Because "no Sicilian can refuse a request on his daughter's wedding day," Corleone, known to his friends and associates as "Godfather", and Tom Hagen (the Corleone family consigliere, or counselor) are preoccupied with hearing requests from friends and associates. Meanwhile, the Don's youngest son Michael, who has returned from World War II service as a highly decorated war hero, tells his girlfriend Kay Adams anecdotes about his father's criminal life, reassuring her that he is not like his family.

Among the guests at the celebration is famous singer Johnny Fontane, a godson of Corleone's, who has come from Hollywood to ask the Godfather's help in getting a movie role that will revitalize his flagging career. Jack Woltz, the head of the studio, will not give Fontane the part, but Don Corleone explains to Johnny: "I'm gonna make him an offer he can't refuse." Hagen is dispatched to California to fix the problem, but Woltz angrily tells him that he will never cast Fontane in the role, which he is perfect for, because Fontane "ruined" a starlet that Woltz favored. The next morning, Woltz wakes up to find the bloody severed head of his prize stud horse in the bed with him.

Upon Hagen's return, the family meets with heroin dealer Virgil "The Turk" Sollozzo, who has influence with the rival Tattaglia family. He asks Don Corleone for political protection and financing to start the mass importation and distribution of heroin but, despite the huge amount of money to be made, Corleone refuses. The Don's oldest son, hotheaded Sonny, breaks ranks during the meeting and expresses interest in the deal. His father, angry at Sonny's dissension in front of a non-family member, later privately rebukes him.

After Don Corleone's refusal, Hagen is abducted by Sollozzo and his henchmen, while the Don himself is badly wounded during an assassination attempt, but survives. Sollozzo persuades Hagen to offer Sonny the deal previously offered to his father, but Sonny refuses to consider the deal, promising a war with the Tattaglias and Sollozzo. The Corleones now prepare for the likelihood of all-out warfare with the rest of the Five Families, who will unite against the Corleones.

Michael, who is recognized by the other Mafia families as a "civilian" in their conflict, visits his father in the hospital, but finds nobody guarding him. Realizing that his father is being set up to be killed, he moves him to another room, calls Sonny with a report, and goes outside to watch the door. After he has bluffed away some of Sollozzo's goons, police cars arrive with the corrupt Captain McCluskey, who breaks Michael's jaw with a single punch. Just then, Hagen shows up with "private detectives" licensed to carry guns to protect Don Corleone.

Following the attempt on his father's life at the Hospital, Michael volunteers to kill Sollozzo and Captain McCluskey, who is acting as Sollozzo's bodyguard. Sonny and the other senior members of the Corleone family are initially amused by Michael's supposed naiveté and Sonny admonishes him for reacting too personally and emotionally. However, Michael convinces them that killing Sollozo and McCluskey is in the family's interests ("It's not personal, Sonny. It's strictly business.")

A meeting between Michael and Sollozo, with McCluskey attending, at a restaurant is arranged, ostensibly to discuss peace. Michael excuses himself to go to the restroom, retrieves a planted revolver, and executes Sollozzo and McCluskey with near-point-blank-range shots to the head. To avoid arrest for the murders, Michael is sent to Sicily, where he lives under the protection of a local Mafia Don. While there, he falls in love, then marries a local girl, Apollonia, who is subsequently murdered during an attempt on Michael's life.

Meanwhile, back in New York, Don Corleone returns home from the hospital and is distraught to learn that Michael was the one who killed Sollozzo and McCluskey. Some months later, in 1948, Sonny severely beats Carlo for hitting Connie. The next time Carlo beats her, Sonny drives off alone to find him and kill him. On the way, he is ambushed and machine-gunned to death.

Instead of seeking revenge for Sonny's killing, Don Corleone meets with the heads of the Five Families to arrange an end to the war. Not only is it draining all of their assets and threatening their survival, but ending the conflict is the only way that Michael can return home safely. Reversing his previous decision, Vito agrees that the Corleone family will provide political protection for Philip Tattaglia's traffic in heroin. At the meeting, Don Corleone realizes that Don Barzini, not Tattaglia, was responsible for the mob war.

With his safety guaranteed, Michael returns from Sicily. More than a year later, he reunites with his former girlfriend, Kay, telling her that he wants to marry her. With the Don semi-retired, Sonny dead and middle brother Fredo considered incapable of running the family business, Michael is now in charge, and he claims that the family business will soon be completely legitimate.

Clemenza and Tessio, two Corleone Family caporegimes (captains) complain that they are being pushed around by the Barzini Family and ask permission to strike back, but Michael refuses. With his father as consigliere, he plans to move the family operations to Nevada and after that, Clemenza and Tessio may break away to go on their own. Michael further promises that Connie's husband, Carlo, is going to be his right hand in Nevada, while Hagen will be the Family's Las Vegas lawyer.

In Las Vegas Michael is greeted by Fredo in the hotel-casino partly financed by the Corleones, run by Moe Greene. Michael explains to Johnny Fontane that the Family needs his help in persuading Johnny's friends in show business to sign long-term contracts to appear at the casino. In a meeting with Moe Greene, Michael offers to buy out Greene but is rudely rebuffed. Greene believes the Corleones are weak and that he can secure a better deal from Barzini.

Michael returns home. In a private meeting, Vito explains his expectation that the Family's enemies will attempt to kill Michael by using a trusted associate to arrange a meeting as a pretext for assassination. Shortly afterwards, Don Vito dies of a heart attack while playing with his young grandson in his tomato garden.

During the funeral, Tessio conveys a proposal for a meeting with Barzini, which identifies him as the traitor that Vito was expecting. Michael arranges the murders of Moe Greene, Philip Tattaglia, Emilio Barzini, Salvatore Tessio, Anthony Stracci, and Ottilio Cuneo, all to take place during the baptism of Connie and Carlo's second son, for whom he will be godfather. After the baptism, Michael confronts Carlo about Sonny's murder and tricks him into admitting his role in setting up the ambush. "Today," Michael tells him, "I settle all Family business." Michael informs Carlo that his punishment is to be excluded from the family business and hands him a plane ticket to exile in Nevada. Carlo gets into a car to go to the airport, and is strangled by Clemenza.

Later, Connie confronts Michael, accusing him of Carlo's murder. Kay questions Michael about Connie's accusation, but he refuses to answer. She insists, and Michael lies, assuring his wife that he had no role in Carlo's death. Kay is relieved by his denial. As the film ends, she watches Clemenza and new caporegime Rocco Lampone pay their respects to Michael, kissing his hand and addressing him as "Don Corleone." The door is closed by new sotto capo (underboss) Al Neri, as she realizes that Michael has become the new Godfather.