Puzo's finest achievement, the one that kept millions of readers turning each page, was his gift for giving each character more personality than just what the book's plot requires of them. His characters have depth: to use a publicist's phrase, they "jump off the page." The smaller, minor characters in any novel are bound to be stereotypes, but Puzo gives all, down to the least significant, some aspect that contradicts their stereotype, hinting at a full, breathing person passing through the story. Kay's father, for instance, only appears in the book for a few pages. He is a New England minister who is approached by the police about his daughter's involvement with organized crime and sexual relations with a suspected murderer. A less intelligent book would have made him act according to type, blowing up with anger or curling with hidden rage.
Puzo has him behave with unexpected gentleness toward his daughter and firmness toward the police, giving readers a sharp little surprise without violating what little we know about this man. From the baker who is delighted with his little part of a Mafia wedding to Neri, the family-oriented hit man, the characters have a human touch that takes them beyond just being tools of the plot.At the next level of characterization Puzo has the three Corleone boys. Independently, none is able to blossom beyond a flat characterization, but it is Puzo's luck or genius to have them all packaged together as a group. Sonny nearly reaches the depths of a vaudevillian comic character with his hotblooded Mediterranean passions: swarthy, oversexed, and impetuous, he seems more like the sort of character that would be created by someone who had never met a real live Italian..