In Greek mythology, Eurystheus was king of Tiryns, one of three Mycenaean strongholds in the Argolid: Sthenelus was his father and the "horsewoman" Nykippe his mother, and he was a grandson of the hero Perseus, as was his opponent Heracles. In the contest of wills between Hera and Zeus over whom the hero would be, who would defeat the remaining creatures representing an old order and bring about the reign of the Twelve Olympians, Eurystheus ("wide strength") was Hera's candidate and Heracles—though his name implies that at one archaic stage of myth-making he had been "Hera's man"— 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–that was sent by Hera, however; further human rather than mythic motivation is supplied by mythographers who note that their repective families families had been rivals for the throne of Mycenae. Details on the Twelve Labours are to be found at the article on Heracles, but Hera was connected with all of the opponents Heracles had to overcome
Heracles' human step-father 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 murdering (a familiar mytheme) the eldest son in the family (Electryon). When Zeus proclaimed the next born descendant of Perseus should get the kingdom shortly before his son Heracles was born, 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.
Eurystheus' third task did not involve killing a beast, but to capture the Cerynian Hind, a golden-horned stag sacred to Artemis. Heracles knew that he had to return the hind as he had promised to Artemis, so he agreed to hand it over on the condition that Eurystheus himself came out and took it from him. Eurystheus came out, but the moment Heracles let the hind go, it sprinted back to her mistress, and Heracles left saying that Eurystheus had not been quick enough.
When Heracles returned with the Erymanthian Boar, Eurystheus was frightened and hid again in his jar and begged Heracles to get rid of the beast; Heracles obliged.
For his seventh labour Heracles captured the Cretan Bull. Heracles used a lasso and rode it back to his cousin. Eurystheus wanted to sacrifice the bull to Hera his patron, who hated Heracles. She refused the sacrifice because it reflected glory on Heracles. The bull was released and wandered to Marathon, becoming known as the Marathonian Bull.
When Heracles brought back the man-eating Mares of Diomedes successfully, Eurystheus dedicated the horses to Hera and allowed them to roam freely in the Argolid. Bucephalus, Alexander the Great's horse, was said to be descended from these mares.
To extend what may have once been ten Labours to the canonical dozen, it was said that Eurystheus didn't count the Hydra, as he was assisted, or the Augean stables as Heracles received payment for his work. For the eleventh labour Heracles had to steal the Apples of the Hesperides; his final labour was to capture Cerberus, the three-headed hound that guarded the entrance to Hades.
After Heracles died, Eurystheus attempted to destroy his many children (the Heracleidae, led by Hyllus), who fled to Athens. He attacked the city, but was soundly defeated, and he and his sons were killed. The stories about the killer of Eurystheus and the fate of his corpse vary, but the Athenians believed it remained on their soil and served to protect the country against the descendants of Heracles, who traditionally included the Spartans and Argives.
After Eurystheus death, the brothers Atreus and Thyestes, whom he had left in charge during his absence, took over the city, the former exiling the latter and assuming the kingship, while Tiryns returned to the overlordship of Argos.
- Kerenyi, Karl, 1959. The Heroes of the Greeks