Donna is a mother trying to adapt after moving her family from New York to rural Castle Rock, Maine. She feels isolated and fears losing her independence to suburban domesticity. This internal frustration recently led her into an extramarital affair with a local artist. She carries immense guilt over the infidelity and struggles to find her footing in a small town.

Cujo is a massive St. Bernard belonging to the Camber family. Originally a sweet and gentle pet who safely played with neighborhood children, his temperament changes drastically after contracting rabies from a bat bite. As his illness progresses, he loses his friendly nature and becomes a violent threat to anyone who crosses his path.

Vic is a relocated New Yorker who co-founded a local advertising agency in Castle Rock. He faces a massive professional crisis when a product dye issue threatens his biggest account. While attempting to save his business, he also learns of his wife's affair, forcing him to choose between salvaging his marriage or focusing entirely on his career.

Tad is the four-year-old son of Vic and Donna Trenton. He suffers from severe anxiety about a monster he believes lives in his room. He relies heavily on his father for a sense of safety, particularly placing his faith in a handwritten poem called the "Monster Words" to ward off evil.

Charity is a meek woman who endures verbal and physical abuse from her husband. After secretly winning the lottery, she gains the financial means to assert a small amount of control over her life. She uses her winnings to buy her husband a gift, bribing him into letting her take their son on a family trip to Connecticut.

Joe is a harsh and controlling mechanic who runs an auto repair shop on his rural Castle Rock property. He dictates the lives of his wife and son with a heavy hand, teaching his boy to adopt a cynical and prejudiced view of the world. He plans a solo trip to Boston while his family goes to Connecticut.

Brett is the ten-year-old son of Joe and Charity Camber. He feels caught between his mother's gentle empathy and his father's abrasive toughness. When he notices his beloved dog looking sick, he chooses to keep quiet about it, fearing his father will cancel his rare opportunity to travel to Connecticut.

Gary is an elderly army veteran living near the Camber property. He leads a quiet, somewhat bitter life but maintains a friendly relationship with his neighbor's dog. His familiarity with animals allows him to quickly recognize the symptoms of rabies.

Roger is the co-founder of Ad Worx, an advertising agency based in Maine. He works tirelessly alongside his partner to brainstorm solutions for a massive food dye scandal involving their primary client, Sharp Cereals.

Steve is a local Castle Rock artist who had a brief affair with a married woman. When the relationship ends, his wounded pride turns into vindictive rage. He actively seeks to destroy his former lover's domestic life by sending a detailed letter about the affair to her husband.

Evelyn, widely known as Aunt Evvie, is the oldest living resident of Castle Rock. She functions as a local harbinger, predicting that the intense heat wave of 1980 will bring terrible and deadly events to the town.

George is a postal worker responsible for the rural delivery routes in Castle Rock. His daily schedule places him in close proximity to various local families, and his route alterations impact the timeline of emergency discoveries.

Holly is a relatively wealthy woman living in Stratford, Connecticut. She offers a sharp contrast to her sister's harsh rural life, providing a comfortable and welcoming environment for her visiting family members.

Jim is a financially comfortable man living in Connecticut. He enjoys the conveniences of his wealth, taking particular pride in store-bought items like a jukebox, which draws quiet criticism from his more industrially minded in-laws.

George is the Sheriff of Castle Rock. He coordinates the local law enforcement efforts when domestic disputes escalate and when residents are reported missing during the chaotic summer heat wave.

Frank Dodd is a deceased serial killer whose legacy continues to haunt Castle Rock long after his death. Though no longer alive, his memory serves as the ultimate boogeyman for the town's children, acting as a lingering symbol of the evil that can hide in plain sight.