A chimpanzee raised alongside Rosemary as part of a familial and research dynamic, Fern's story is recounted through human memories, highlighting her unique relationship with Rosemary and the Cooke family.

A psychologist focused on his professional standing, Vince views life scientifically and is emotionally distant within his family. His research and decisions significantly impact Rosemary's childhood and family dynamics.

A nurturing figure with deep emotions, Rosemary's mother manages the household and cares for Rosemary and Fern. She becomes involved in animal rights activism later in the story.

Rosemary's older brother with a strong dedication to animal rights, Lowell is portrayed as rebellious and driven by his passion for activism, often prioritizing it over family connections.

A vibrant and boundary-pushing college student with a theatrical demeanor, Harlow forms an unusual friendship with Rosemary and is known for her persuasive and assertive personality.

Initially Harlow’s boyfriend, Reg exhibits a complex confidence influenced by societal norms, later shifting to a different role in Rosemary’s life. He is often perceived as rude and assertive.

The manager of Rosemary's apartment complex, Ezra is often absent or unhelpful, with a particular affinity for conspiracy theories and a desire for intrigue and heroism in his life. He is infatuated with Harlow.