Aeacus (/ˈiːəkəs/; also spelled Eacus; Greek: Αἰακός) was a mythological king of the island of Aegina in the Saronic Gulf. He was the father of Peleus, Telamon and Phocus and was the grandfather of Achilles and Telemonian Ajax.
Aeacus was the son of Zeus and Aegina, a daughter of the river-god Asopus. He was born on the island of Oenone or Oenopia, where Aegina had been carried by Zeus to secure her from the anger of her parents; afterward, this island became known as Aegina. According to some accounts, Aeacus was a son of Zeus and Europa. Some traditions related that, at the time when Aeacus was born, Aegina was not yet inhabited, and that Zeus either changed the ants (μύρμηκες) of the island into the men (Myrmidons) over whom Aeacus ruled, or he made the men grow up out of the earth.Ovid, on the other hand, supposed that the island was not uninhabited at the time of the birth of Aeacus, instead stating that during the reign of Aeacus, Hera, jealous of Aegina, ravaged the island bearing the name of the latter by sending a plague or a fearful dragon into it, by which nearly all its inhabitants were carried off. Afterward, Zeus restored the population by changing the ants into men.