The Lost Hero is an American fantasy-adventure novel written by Rick Riordan, based on Greek and Roman mythology. It was published on October 12, 2010, and is the first book in The Heroes of Olympus series, a sequel to the Percy Jackson & the Olympians series. It is preceded by The Last Olympian of Percy Jackson & the Olympians and followed by The Son of Neptune. The novel has since been translated into many languages and released as a hardcover, e-book, audiobook and paperback.

Richard Russell Riordan Jr. is an American author, best known for writing the Percy Jackson & the Olympians series. Riordan's books have been translated into forty-two languages and sold more than thirty million copies in the United States. 20th Century Fox adapted the first two books of his Percy Jackson series as part of a series of films in which Riordan was not involved. Riordan currently serves as a co-creator and executive producer on the television series adaption of the book series that was released on Disney+ in 2023. Riordan's books have also spawned other related media, such as graphic novels and short story collections.