The Trials of Apollo series is author Rick Riordan’s third group of novels set in the Percy Jackson universe. In this universe, Greek and Roman gods are real, magic and magical creatures exist, and the protagonists are usually demigods, children of gods with human beings. The concept of demigods is inspired by Greek mythology, where human descendants of gods often play the part of heroes, interceding with gods on the behalf of humanity. Examples of heroes in mythology are Hercules, the son of the arch-god Zeus and a human woman, and Perseus, the mortal son of Poseidon, the god of water and oceans. Percy Jackson, protagonist of Riordan’s flagship Percy Jackson series, is modeled after Perseus.

In the Trials of Apollo pentalogy, Apollo, the god of the sun, poetry, music, and healing, has been “punished” to become a human by his father Zeus. To regain his immortality, Apollo must complete a series of trials to free Oracles or sources of prophecy. The Oracles have been seized by an evil trio of resurrected emperors from ancient Rome who call themselves the Triumvirate. Behind the Triumvirate is Python, a legendary monstrous serpent and the arch-nemesis of Apollo.