Augeas was King of Ellis, and father of Epychaste. He was most famously known for his stables which housed the single greatest amount of cattle and had never been cleaned until the time of Herakles.
Herakles's fifth labor was to clean the Aegean stables. This was an almost impossible job because the cows were immortal, it hadn't been cleaned in 30 years, the cows created an enormous amount of dung and there were 30,000 of them. Augeas told Herakles that if he could complete the task in a day then he would give him 10 of the cows.
Herakles finished the task by rerouting the two rivers, Alpheus and Peneus so that they would wash out the filth. When the task was done Augeas refused to hold up his side of the bargain, and Herakles killed him. He also gave the kingdom of Augeas to his son Phyleus.