The Godfather is a movie about the life lived in a world of gangsters. Michael Cicerone is the son of Vito Cicerone who plays "the godfather".
Michael is a successful and level-headed man who went to college and enlisted in the marines to avoid falling into the entrapments of the family business.However, throughout the film Michael not only gets involved in the mafia but takes the negatives of this world o more extremes than does his father, making himself into a mean and cruel man that Vito Cicerone was not. Michael is an honorable man at the beginning of The Godfather until his father is shot but not assassinated. Veto's security is taken away so that men can try to come and murder him while at the hospital. Michael prevents this, but in doing so he welcomes his downfall into the man he does not want to be.
As Michael shoots the crooked cops, we see his other side emerge. Michael leaves for Sicily, falls in love and gets married. This could have saved him from what he has already done and could prevent him from a place of no return in the mafia world. But when Apollonian is blown up in a car that was meant for him, it sets Michael off especially with learning also of his brother Sonny's murder. Michael is now fully involved in the family business.
We see this as he and his father plan to little by little wipe out all the Dons of the other families.