Acastus | King of Iolcus
Acastus, in Greek mythology was the son of Pelias and king of Iolco in Thessaly.
Family
His father, Pelias, son of Posidon (Poseidon) and Tyre, married Anaxibia, daughter of Bias or Philomachus, daughter of Amphion, and had a son, Acastus, and several daughters, Pisidice, Pelopia, Hippotoe, and Alcestes.
Pelias, out of fear of Jason, the son of his half-brother Esam, sent him to Colchis to fetch the golden fleece. Acastus was one of the Argonauts on this expedition.
During the expedition of the Argonauts, Pelias wanted to kill Esam, but the latter asked to commit suicide, which he did by drinking the blood of the sacrificed bull; then Jason's mother committed suicide by hanging, leaving an infant son Promachus, who was murdered by Pelias.
When Jason returned and handed the golden fleece to Pelias, he wanted revenge, but lacking the strength, he went into exile and asked Medea to devise a plan. She then convinced Pelias' daughters that if they cut their father and cooked him, he would be young again-and he died that way.
Acastus, however, buried their father and drove Jason and Medea out of Iolco. According to another version, Jason handed the kingdom over to Acastus and took care of Pelias' daughters, causing them to marry men of renown.
King of Iolco
His wife Astidamia fell in love with Peleus. Peleus had been purified by Ahasto after he had accidentally killed his father-in-law Eurithion during the hunt for the Chalidonian boar.
When Peleus rejected her, Astidamia sent a message to Peleus' wife, Antigone, that Peleus was to marry Ahasto's daughter, Sterrope; Antigone committed suicide when she heard the news. She then accused him of raping her. Acastus could not kill a man he had purified, took him on a hunt, and abandoned him, swordless. He would be killed by the centaurs, but was saved by Quirão, who returned his sword.
End of reign
Peleus, having fathered Achilles, was helped by Jason and the twins Castor and Pollux. They sacked Iolco and dismembered Astidamia. The kingdom then passes to Jason's son, Thessalonus.
In the text attributed to Dictis of Crete, Acastus is king in Thessaly until after Odysseus returns to Ithaca. Neoptolemus, while among the Molossians repairing their ships, discovers that Acastus had driven out his grandfather Peleus.
Neoptolemus finds his grandfather hiding in a cave, discovers what had happened, and murders two of Acastus' sons, Melanippus and Plisthenes, who were hunting in the area.
Then, wearing the robes of Mestor, son of Priam whom he had brought as a slave from Troy, he introduced himself to Acastus as if he were Mestor, and said that Neoptolemus was tired, and sleeping in the cave. Acastus, wanting to take revenge on his enemy, went to the cave, where Thetis rebuked him for his crimes against the house of Achilles and against the gods. Tethis, however, did not let Neoptolemus kill Acastus, and Acastus renounced the kingdom.