Eurystheus was a mythical king of Mycenae and grandson of the hero Perseus. He is notable mainly for the Twelve Labors he imposed on Heracles, whom he hated mainly because their families had been rivals for the throne. (See Heracles for details on the Twelve Labors)
Heracles' step-father Amphitryon was also a grandson of Perseus, and since Amphitryon's father (Alcmaeus) was older than Eurystheus' father (Sthenelus), ought to have received the kingdom, but Sthenelus had banished Amphitryon for accidentally murdering the eldest in the family (Electryon), and 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 having Eurystheus born prematurely.
The 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 bronze jar and from that moment forth all labors were communicated to Heracles through a herald, Copreus.
His second labour was to slay the Lernean Hydra, a formidable snake-like beast that possessed nine heads and poisonous breath. For this task Heracles took his nephew, Iolaus, with him 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 was greatly angered to find that Heracles had managed to escape death for a second time and so decided to spend more time upon thinking up a third task that would spell doom for the hero. The third task did not involve killing a beast, as it had already been established that Heracles could survive even the most fearsome opponents, so Eurystheus decided to make him capture the Cerynian Hind, a beautiful creature sacred to Artemis the chaste goddess of the hunt and moon. Upon bringing the hind to Eurystheus, he was told that it was to become part of the King's menagerie. 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. The King 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.
His fourth Labour was to capture the Erymanthian Boar. After Heracles caught it, he went back to Eurystheus who was frightened and hid in a large jar. He begged Heracles to get rid of the beast; Heracles obliged.
The fifth task set to Heracles was to clean the Augean stables in a single day. The reasoning behind this labour was twofold, firstly, all the previous labours only exalted Heracles in eyes of the people so this one would surely degrade him; secondly, the stables of Augeas housed the single greatest number of cattle in the country and having never been cleaned this task was surely impossible. Heracles, however, rerouted a river and cleaned the stables quickly and easily.
For his sixth task Heracles had to drive away the Stymphalian Birds, fearsome creatures with bronze beaks that terrorised the lake that they had come to inhabit some years previously. Some accounts say that they had razor sharp feathers that could be fired at attackers.
For his seventh labour Heracles was told to capture the Cretan Bull. According to various sources, it was the bull that carried away Europa or the bull Pasiphae fell in love with. The King of Crete, Minos, gave Heracles permission to take the bull away. It had been wreaking havoc on Crete. Heracles used a lasso and rode it back to his cousin, Eurystheus. Eurystheus wanted to sacrifice the bull to Hera, 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.
The eighth labour of Heracles was to steal the Mares of Diomedes, however, Heracles was not aware that the magnificent horses were man-eating. When Heracles brought them back successfully, Eurystheus dedicated the horses to Hera and allowed them to roam freely around Argos. Bucephalus, Alexander the Great's horse, was said to be descended from these mares.
To acquire the belt of Hippolyte, queen of the Amazons was Heracles's ninth task. This task was at the request of Eurystheus' daughter, Admete.
For his tenth labour Heracles had to obtain the Cattle of Geryon. Geryon had three sets of legs and three bodies all joined at the waist, and his hound was Orthus the two-headed brother of Cerberus.
Although he only had to perform ten labours, Eurystheus didn't count the Hydra as he was assisted, or the Augean stables as he received payment for his work. For the eleventh labour Heracles had to steal the Apples of the Hesperides, a wedding gift from Hera to Zeus, guarded by the dragon Ladon who never slept and the Hesperides, nymphs who were the daughters of Atlas.
His final labour was to capture Cerberus, the three-headed hound that guarded the entrance to Hades. It is also said that Cerberus had a mane of serpents and a snake for a tail.
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 body 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 him, 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 Tyrins returned to the kingdom of Argos.