Cujo was a St. Bernard, owned by the Camber Family. During the events of the novel, Cujo was bitten by a bat and got rabies from it. For the next few days, he became more and more dangerous, eventually killing Gary Pervier and Joe Camber. When Donna Trenton and her son, Tad, go to the Cameber's farm for an auto repair, they are attacked by the dog and spend three days in their car hiding from him. While they was stuck in the car, Cujo hears sounds like when the phone ring , Cujo acts crazy and continues to haunt Donna and her son Tad, while being stuck in the car.
Cujo was later killed when he tries to attack Donna, but was killed by a dead Sherrif's revolver.