Acastus

Argonaut. Acastus was the son of Pelias and Anaxibia or Phylomachus.

Acastus joined his cousin Jason in the quest for the golden fleece. When Medea tricked his sisters into murdering their father, Acastus drove Jason and Medea into exile for causing his father's death. He became king of Iolcus.

At his father's funeral, Acastus invited many heroes of Greece to take part in the Games, perhaps the largest ever.

When another fellow Argonaut, Peleus, arrived in Iolcus, Acastus purified Peleus for the accidental killing of his father-in-law, Eurytion, during the Calydonian boar hunt.

While Peleus remained as a guest in Iolcus, Astydameia or Hippolyte, Acastus' wife, fell in love with her husband's guest and tried to seduce Peleus. Peleus' rejected her, causing her to become enraged. In secret, Astydameia told her husband that Peleus had tried to violate her. Since the gods frowned upon killing a guest, Acastus secretly plotted Peleus' death.

He took Peleus on a hunting trip. While Peleus slept in camp, Acastus stole Peleus' magic sword and hid it. Acastus then left the sleeping hero defenceless, in the hostile territory of the Centaurs. But Peleus was rescued by a friendly and wise Centaur named Cheiron, who helped him recover the sword.

Peleus later returned to Iolcus with an army and, aided by the heroes, Jason and the Dioscuri (Castor and Polydeuces), he captured Iolcus, then killed Acastus and his lying wife. Acastus' son Thessalus succeeded his father (or he was possibly a son of Jason and Medea) and ruled Iolcus. Thessalus was the eponym of Thessaly.