Eurystheus

Perseus' son Electryon ruled Mycenae until he was probably killed accidentally by his nephew and son-in-law, Amphitryon. Sthenelus took the throne that should have belonged to Amphitryon. When the god Zeus was expecting the birth of his son Heracles by Alcmene, wife of Amphitryon, the god expected his son to rule both Mycenae and Tiryns. Zeus boasted that the descendant of Perseus to be born that day would rule Argolis. The goddess Hera, the jealous wife of Zeus, delayed Heracles birth while she hurried Sthenelus' son Eurystheus (Εὐρυσθεύς) to be delivered first. Therefore, Eurystheus succeeded his father to the throne rather than the god's own son.

Eurystheus was married to Antimache and was the father of Admeta or Admete, and of four sons – Alexander, Eurybius, Iphimedon, Mentor and Perimedes.

Eurystheus was born a weakling, because Hera had hurried his birth, so that he became the future king instead of his cousin Heracles. Eurystheus was born two months premature. Because he was weak, Eurystheus became a notorious coward. He was the exact opposite of his heroic cousin Heracles, who would win glories and later, immortality.

Eurystheus ruled Mycenae and Tiryns. Heracles had to perform the Twelve Labours for Eurystheus, to atone for the murder of his own sons. When Heracles brought the Erymanthian Boar alive, Eurystheus hid in a bronze vase. Eurystheus also ordered that Heracles should display all future successful tasks (with dangerous animals) outside of the city's walls. See the fourth labour of Heracles.

Eurystheus never felt secure on his throne, even when Heracles was serving him in the Twelve Labours. Later, Eurystheus banished Heracles from Tiryns, fearing that the hero might want the throne for himself.

Even with his cousin's death, he still didn't feel secure in his kingdom, so Eurystheus persecuted Heracles' other surviving children. Heracles children couldn't stay in Trachis, because Ceyx was too weak to defend them. Iolaus, nephew of Heracles, was their only protector, and guided them to Athens as suppliants.

According to Euripides' tragedy, Demophon, son of the Athenian hero Theseus, was king of Athens. Demophon agreed to aid the Heraclids who were actually his cousins, with his army. They confronted and defeated Eurystheus' army at Marathon. A miracle was witnessed that day as Iolaus regained his youth for a day, during this battle; a gift from Hebe, Heracles' new wife. It was Iolaus who captured Eurystheus and brought the defeated king to his grandmother Alcmene, mother of Heracles. It was Alcmene who gouged out Eurystheus' eyes. (See Heraclids for a fuller tale about the children of Heracles and later descendants.)

Eurystheus' cousins, Atreus and Thyestes, the sons of Pelops, king of Pisa, succeeded him on the throne of Mycenae. See House of Atreus.