The Darkest Hour is a children's fantasy novel, the sixth and last book in the original Warriors series by Erin Hunter, featuring the fictional character Firestar, a cat. The series revolves around a group of wild cats living in four Clans, ThunderClan, RiverClan, WindClan, and ShadowClan. It was published on 1 October 2004, by HarperCollins. The story chronicles the events directly after A Dangerous Path and leads to the final battle for the forest.

Erin Hunter is a collective pseudonym used by the authors Victoria Holmes, Kate Cary, Cherith Baldry, Clarissa Hutton, Inbali Iserles, Tui T. Sutherland, and Rosie Best in the writing of several juvenile fantasy novel series which focus on animals and their adventures. Notable works include the Warriors, Seekers, Survivors, Bravelands, and Bamboo Kingdom book series. For each book, Holmes creates the plot and the others take turns writing the books. Dan Jolley, though not an official Erin Hunter author, also writes the stories for manga published under the Hunter name. James L. Barry, Bettina M. Kurkoski, and Don Hudson are included under the pseudonym as the illustrators of the Warriors mangas. Natalie Riess and Sara Goetter are also included as the illustrators of the upcoming graphic novel adaptation of The Prophecies Begin.