The One and Only Ivan is a 2012 novel written by Katherine Applegate and illustrated by Patricia Castelao. It is about a silverback gorilla named Ivan who lived in a cage at a mall, and is written from Ivan's point of view. In 2013 it was named the winner of the Newbery Medal. It has won several other awards and is currently nominated to several reading lists. It was followed in 2020 by The One and Only Bob, presented from the point of view of Ivan's best friend, the dog Bob. A second sequel, The One and Only Ruby, was published in 2023.

Katherine Alice Applegate, known professionally as K. A. Applegate, is an American young adult and children's fiction writer, best known as the author of the Animorphs, Remnants, and Everworld book series. She won the 2013 Newbery Medal for her 2012 children's novel The One and Only Ivan. Applegate's most popular books are science fiction, fantasy, and adventure novels. She won the Best New Children's Book Series Award in 1997 in Publishers Weekly. Her book Home of the Brave has won several awards. She also wrote a chapter book series in 2008–09 called Roscoe Riley Rules.