In Greek mythology, Polydorus (Ancient Greek: Πολύδωρος) was the eldest son of Cadmus and Harmonia and king of Thebes. His sisters were Semele, Ino, Agave, and Autonoë.
Upon the death of Cadmus, Pentheus, the son of Echion and Agave, the daughter of Cadmus, ruled Thebes for a short time until Dionysus prompted Agave to kill Pentheus. Polydorus then succeeded Pentheus as king of Thebes and married Nycteïs, the daughter of Nycteus. When their son Labdacus was still young, Polydorus died of unknown causes, leaving Nycteus as his regent. In Pausanias's history, Polydorus' rule began when his father abdicated, but this is the only source for such a timeline.