Herb Clutter, the father of the Clutter family, is a religious Methodist, a strict but loving father, and a well-to-do wheat farmer who owns River Valley Farm. He is a major figure in the wheat farming industry, having served on the Federal Farm Credit Bureau under Eisenhower and the Kansas Conference of Farm Organizations, and was involved in founding a union for wheat farmers. Clutter has had to take on many household and parenting duties, including cooking, because his wife, Bonnie, is frequently debilitated by depression. He is a tough man regarding rules but has a generous, trusting spirit.
Bonnie Clutter is the mother of the Clutter family. She is a frequently depressed woman who has gone through several hospitalizations at psychiatric hospitals. She sleeps in an extra single bedroom upstairs near the children and often avoids social situations. Her daughter's friends are a bit uncomfortable around her.
Nancy Clutter is described by everyone who knew her as the "town darling." She is an excellent student, a genuinely nice person, a tutor to her peers and younger children, an award-winning baker, president of her class, and leader of her 4-H club and her Young Methodists League group. She is an accomplished musician, actress, and seamstress as well. She is dating Bobby Rupp, a basketball star, and her best friends are Susan Kidwell and Nancy Ewalt.
Kenyon Clutter is a bit of a loner. He is quiet, intelligent, tall, and lanky, but not coordinated enough to excel at sports, which means that he ends up spending a lot of time alone. He has one close friend, Bob Jones, with whom he had hunted rabbits and ducks until Bob started dating a girl. Kenyon is said to be sensitive and "lives in a world of his own."
Perry Smith, an ex-convict released on parole, is a man who needs another man to follow. He idolizes other men almost to the point of romance, though he dislikes talk of sex and people who cannot control themselves sexually. He was severely abused as a child, by both his parents and nuns at an orphanage where his alcoholic mother left him. He is always in pain because of a leg injury from a motorcycle accident and is addicted to aspirin. Soft-spoken, he seems nice to most people who meet him, but if someone angers him he reacts violently, striking out at whoever is near. He is said by psychologists to be a paranoid schizophrenic.
Dick Hickock, an ex-convict out on parole, comes from a loving family. He was a good student and athlete but was in a car accident in which he had a severe head injury, which made his face look like it had been sliced in half and put back together badly. Psychologists later theorized that this accident caused brain damage, which made self-control impossible for Hickock. His parents said after the accident that Hickock began engaging in criminal behavior, writing bad checks and stealing. He has become the kind of person who runs over dogs on purpose. He had married a woman named Carol and, despite his love for her, cheated on her with a second woman who became his second wife because she was pregnant. They had two more children and then she divorced him. He is constantly on the prowl for blonde women, and also has an attraction to very young girls, which he is ashamed of but cannot control. Dick is the one who comes up with the plan to rob and kill the Clutters, his most violent scheme to solve his money problems.
Alvin Dewey is the lead investigator for the Kansas Bureau of Investigation (KBI) on the Clutter case. He has known the Clutters for a long time and considered them friends. Having seen what had been done to them and knowing how much they suffered, Dewey becomes obsessed by the case, and his home life and health suffer for it. He is criticized for not moving fast enough on the case, but the killers clear nearly all evidence from the scene of the crime.