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.

Her novel Crenshaw spent over twenty weeks on the New York Times children's bestseller list, and her first middle-grade stand-alone novel, the award-winning Home of the Brave, continues to be included on state reading lists, summer reading lists, and class reading lists. Katherine has written three picture books: The Buffalo Storm; The Remarkable True Story of Ivan, the Shopping Mall Gorilla (often used as a companion book to The One and Only Ivan for younger readers); and Sometimes You Fly. For beginning readers, Katherine wrote Roscoe Riley Rules, a seven-book series. With her husband, Michael Grant, Katherine co-wrote various works.