The One and Only Books

Read the four novels in order: The One and Only Ivan, The One and Only Bob, The One and Only Ruby, and The One and Only Family. Each book changes narrator, but later stories revisit earlier events and relationships, so publication order gives the emotional history its intended shape.

Ivan is a nonfiction picture book about the real gorilla who inspired the first novel. The Littlest Elephant is a picture-book adaptation of Ruby's story for younger readers. Both can extend a family's reading, but neither replaces the four-novel sequence or counts as book #5. The separate I Can Read books are movie tie-ins rather than continuations of Katherine Applegate's novels.

Sources: Katherine Applegate's official books page, Author announcement of the fourth and final novel, Author FAQ about the real Ivan.

The novels address animals kept in cages, neglect and mistreatment, separation from family, poaching, dangerous weather, injury, death, and grief. Ruby remembers the killing of her mother, and characters carry painful memories even after reaching sanctuary. The language is accessible and the violence is not graphic, but sensitive animal lovers may find the losses intense.

Compassion, chosen family, advocacy, and the difference between captivity and a safe sanctuary anchor the series. Applegate also distinguishes the fictional Ivan's voice from the real gorilla's life, making the nonfiction picture book a useful follow-up for families who want that context.