William’s mother, who supports him through his grief and separation from his father, fosters a new relationship with Stephen, and helps fight for Riley's wellbeing.

William’s father, who is mostly absent and secretive about his new romantic relationship, but attempts to reconnect with William during difficult times.

The Halstons' neighbor, who deeply loves her horse, the Sultan, and is opposed to keeping Riley after he causes harm to the horse.

William’s best friend, who is mature, supportive in his campaign to save Riley, and offers a balanced perspective on the situation.

A 12-year-old who bullies William, harbors trauma and fear of dogs, and initially opposes Riley due to his own past experiences with dogs.

An employee at the pound where Riley was adopted, who becomes significant in Dorothy’s life and represents change for William.