In Greek mythology, Eurystheus (pronounced /jʊrɪsˈθiəs/, Εὐρυσθεύς meaning “broad strength” in folk etymology and pronounced [eu̯rystʰěu̯s]) was king of Tiryns, one of three Mycenaean strongholds in the Argolid, although other authors including Homer and Euripides cast him as ruler of Argos: Sthenelus was his father and the “victorious horsewoman” Nicippe his mother, and he was a grandson of the hero Perseus, as was his opponent Heracles. He was married to Antimache, daughter of Amphidamas. In the contest of wills between Hera and Zeus over whose candidate would be hero, fated to defeat the remaining creatures representing an old order and bring about the reign of the Twelve Olympians, Eurystheus was Hera’s candidate and Heracles — though his name implies that at one archaic stage of myth-making he had carried “Hera’s fame” — was the candidate of Zeus. The arena for the actions that would bring about this deep change are the Twelve Labors imposed on Heracles by Eurystheus. The immediate necessity for the Labours of Heracles is as penance for Heracles’ murder of his own family, in a fit of madness, which had been sent by Hera; however, further human rather than mythic motivation is supplied by mythographers who note that their respective families had been rivals for the throne of Mycenae. Details of the individual episodes may be found in the article on the Labours of Heracles, but Hera was connected with all of the opponents Heracles had to overcome.
Heracles’ human stepfather Amphitryon was also a grandson of Perseus, and since Amphitryon’s father (Alcaeus) was older than Eurystheus’ father (Sthenelus), he might have received the kingdom, but Sthenelus had banished Amphitryon for accidentally killing (a familiar mytheme) the eldest son in the family (Electryon). When, shortly before his son Heracles was born, Zeus proclaimed the next-born descendant of Perseus should get the kingdom, Hera thwarted his ambitions by delaying Alcmene’s labour and having her candidate Eurystheus born prematurely.
Heracles’ first task was to slay the Nemean Lion and bring back its skin, which Heracles decided to wear. Eurystheus was so scared by Heracles’ fearsome guise that he hid in a subterranean bronze winejar, and from that moment forth all labors were communicated to Heracles through a herald, Copreus.
For his second labour, to slay the Lernaean Hydra, Heracles took with him his nephew, Iolaus, as a charioteer. When Eurystheus found out that Heracles’ nephew had helped him he declared that the labour had not been completed alone and as a result did not count towards the ten labours set for him….