Aeacus (ē´əkəs), in Greek mythology, son of Zeus and the nymph Aegina. He was the father of Peleus and Telamon. After a plague had nearly wiped out the inhabitants of his land, Zeus rewarded the pious Aeacus by changing a swarm of ants to men (known as Myrmidons). According to one legend, Aeacus and his people assisted Apollo and Poseidon in building the walls of Troy. After Aeacus' death, Zeus made him one of the three judges of Hades.