Polydorus (son of Cadmus)

In Greek mythology, Polydorus or Polydoros (Πολύδωρος means 'many-gift[ed]') was a king of Thebes.

Family
Polydorus was the youngest and only male child of Cadmus and Harmonia, his sisters were Autonoë, Ino, Agave and Semele. He was the father of Labdacus by Nycteïs, the daughter of Nycteus. "Last of all Harmonia added a little son to the brood of sisters, and made Cadmos happy – Polydoros, the morning star of the Aonian nation, younger than rosy cheek Semele."

Mythology
Upon the death of Cadmus, Pentheus, the son of Echion and Agave, after banishing Polydorus ruled Thebes for a short time until Dionysus prompted Agave to kill Pentheus. Polydorus then succeeded Pentheus as king of Thebes and married Nycteïs. When their son Labdacus was still young, Polydorus died of unknown causes, entrusting his father-in-law Nycteus to care the infant prince and to be his regent.

In Pausanias's history, Polydorus' rule began when his father abdicated the throne and together with his mother Harmonia migrated to the Illyrian tribe of the Enchelii, but this is the only source for such a timeline. It is also said that along with the thunderbolt hurled at the bridal chamber of Semele there fell a log from heaven. This log was adorned by Polydorus with bronze and called it Dionysus Cadmus.

A different account by Diodorus stated that the Thebans were exiled a second time (the first time during the reign of Cadmus) for Polydorus came back and was dissatisfied with the situation because of the misfortunes that had befallen Amphion, the previous king, in connection with his children.