The entire narrative of "The Godfather" is built around the tragic transformation of Michael Corleone. Initially a war hero and outsider, he is drawn into the family's criminal enterprises after an attempt on his father's life. His first major turning point is his calculated murder of Virgil Sollozzo and the corrupt police Captain McCluskey in an Italian restaurant. This act forces him into exile in Sicily, where he marries a local woman, Apollonia, who is then tragically killed by a car bomb intended for him. This loss further hardens him.
Upon his return to America, and following the brutal murder of his older brother Sonny at a causeway tollbooth, Michael assumes control of the family business under the tutelage of his aging father. The film's climax is a masterfully edited sequence known as the "baptism massacre." While Michael stands in a church as the godfather to his sister Connie's child, he has orchestrated the simultaneous assassinations of the heads of the five rival families and other key enemies. Moe Greene is shot through the eye in a massage parlor, Don Cuneo is trapped and killed in a revolving door, and the heads of the Barzini and Tattaglia families are also eliminated.
Following this consolidation of power, Michael confronts his brother-in-law, Carlo, revealing he knows Carlo conspired with Barzini to set up Sonny's murder. After extracting a confession, Michael has Carlo garroted in a car. He also has the disloyal capo, Tessio, taken away to be killed after Tessio revealed himself as a traitor. The final, chilling scene shows Michael lying to his wife Kay, denying his involvement in Carlo's death. Moments later, Kay watches as his men pay their respects, calling him Don Corleone, before the office door is shut, closing her out of his world completely. This ending solidifies his complete descent into the role of a ruthless, isolated, and powerful crime lord, a destiny he once desperately tried to avoid.