The King Must Die is a novel by Mary Renault about the life of Theseus, a character in ancient Greek mythology. In the novel, Mary Renault traces the life of Theseus from his childhood to his adult life. The author gives a realistic perspective on the story, rather than writing a long retelling of the original myth. She also molds the character of Theseus into an underdog, instead of the bronze-age giant as he is often portrayed.