In Greek mythology, King Diomedes of Thrace was the son of Ares and Cyrene. He lived on the shores of the Black Sea, ruling the warlike tribe of the Bistones, and was infamous for his man-eating horses. To complete the eighth of his Twelve Labours, Heracles stole these mares, slaying Diomedes in the process. He is distinct from the Argive Diomedes, son of Tydeus.
Adapted from Wikipedia, "Diomedes of Thrace" · CC BY-SA 4.0
I.Family
Diomedes of Thrace was the son of the god Ares and Cyrene, who is said to be the daughter of Hypseus, King of the Lapiths.
He lived on the shores of the Black Sea, ruling the warlike tribe of the Bistones. Because he was the son of the god of war, he was a formidable opponent: even Heracles, said to possess unmatched strength, faced a long and reasonably even match against him.
II.Mythology
Heracles encounters King Diomedes through performing his eighth labour. Eurystheus, King of Tiryns and Heracles' cousin, had sent Heracles to capture the Mares of Diomedes after he had completed his seventh labour, capturing the Cretan Bull. Heracles travelled to the shores of the Black Sea to meet King Diomedes.
King Diomedes was a savage; he enjoyed feeding strangers and prisoners to his mares. They did not like the taste of oats and grain; instead they feasted on human flesh, which their master gave them willingly. His mares could not be controlled; they were savage, just like the king. They could not be tethered by regular rope, but needed to be chained to a bronze manger so they would not escape.
Upon arrival, knowing how Diomedes treats strangers, Heracles wrestles with him, trying to bring him to the stables where the mares live. Diomedes eventually loses and is brought to the mares' manger, where they devour him. It is said that this cures them of their hunger for human flesh; all they had longed for was their master's blood. They become calm and controllable, and Heracles is able to bring them back to Tiryns to show Eurystheus the completion of his eighth labour.
Eurystheus dedicates the mares to Hera, goddess of marriage, women and childbirth. Once dedicated they were released and free to roam Argos, and one of their descendants is said to be the horse of Alexander the Great. In other translations it is said that the mares are freed to Mount Olympus, where some were eaten by wild beasts.
Other versions of the story claim that Heracles was accompanied by a band of volunteers to assist in acquiring the mares. Rather than wrestling Diomedes alone, Heracles entrusts the mares to a young boy named Abderos. While Heracles and his men defeat Diomedes and his Bistone army, young Abderos is unable to control the mares and is killed in the process. Grieved by his fate, Heracles builds a city named Abdera in his name. Other versions may also include the addition of a chariot: either Heracles attaches the mares to his chariot to tame them, or he takes them along with the chariot of Diomedes.
III.Namesake
Diomedes Lake in Antarctica is named after Diomedes of Thrace.