Michael Corleone (Al Pacino)’s Timeline and Summary

After serving in World War II, he attends his sister's wedding with Kay and seems committed to avoiding a life of crime.
After the near-assassination of his father, Michael decides to whack two of the men responsible, personally. He does and flees to Sicily.
In Sicily, Michael falls in love, courting and marrying Apollonia.
But she dies after a car bomb blows her to pieces. (Frowny face). After Michael's brother Sonny is also killed, he returns to America, his father having made a truce with the Tattaglias.
Michael becomes the new acting Don. He gradually asserts his power, talking smack to Moe Greene and identifying the traitors in his midst, like Tessio and Carlo.
After his father dies, Michael really is the new Godfather.
He cleans house, killing off the traitors, along with his major enemies in the other families.
By the movie's end, he's fully entered his role as a murderous mafia don, while trying to hide his true business from Kay, his new wife.