Summary:

King Diomedes (Διομήδης) of Thrace

Thrace

Thrace is a historical and geographic area in southeast Europe. As a geographical concept, Thrace designates a region bounded by the Balkan Mountains on the north, Rhodope Mountains and the Aegean Sea on the south, and by the Black Sea and the Sea of Marmara on the east...

 was a giant

Giant (mythology)

The mythology and legends of many different cultures include monsters of human appearance but prodigious size and strength. "Giant" is the English word commonly used for such beings, derived from one of the most famed examples: the gigantes of Greek mythology.In various Indo-European mythologies,...

, the son of Ares

Ares

Ares is the Greek god of war. He is one of the Twelve Olympians, and the son of Zeus and Hera. In Greek literature, he often represents the physical or violent aspect of war, in contrast to the armored Athena, whose functions as a goddess of intelligence include military strategy and...

 and Cyrene

Cyrene (mythology)

In Greek mythology, as recorded in Pindar's 9th Pythian ode, Cyrene was the daughter of Hypseus, King of the Lapiths. When a lion attacked her father's sheep, Cyrene wrestled with the lion. Apollo, who was present, immediately fell in love with her and kidnapped her. He took her to North...

. He lived on the shores of the Black Sea

Black Sea

The Black Sea is bounded by Europe, Anatolia and the Caucasus and is ultimately connected to the Atlantic Ocean via the Mediterranean and the Aegean seas and various straits. The Bosphorus strait connects it to the Sea of Marmara, and the strait of the Dardanelles connects that sea to the Aegean...

 ruling the warlike tribe of Bistones

Bistoni

Bistones is the name of a Thracian people who dwelt between Mount Rhodopé and the Aegean Sea, beside Lake Bistonis, near Abdera. From the worship of Dionysus in Thrace, female Bacchanals were sometimes called Bistonides, just as in some Latin poems, Edonis refers to female Bacchanals...

. He is known for his four man-eating horses

Mares of Diomedes

The Mares of Diomedes, also called the Mares of Thrace, were four man-eating horses in Greek mythology. Magnificent, wild, and uncontrollable, they belonged to the giant Diomedes , king of Thrace, a son of Ares and Cyrene who lived on the shores of the Black Sea...

, which Heracles

Heracles

Heracles ,born Alcaeus or Alcides , was a divine hero in Greek mythology, the son of Zeus and Alcmene, foster son of Amphitryon and great-grandson of Perseus...

 stole in order to complete the eighth of his Twelve Labours, slaying Diomedes in the process.

King Diomedes in The Labours of Heracles:

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. He was said to have been the son of the god Ares and Cyrene, who is said to be the daughter of Hypseus, King of the Lapiths. 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; instead they needed to be tethered to a bronze manger by chains, so they would not escape.

Upon arrival Heracles, knowing how King Diomedes treats strangers, wrestles with him, trying to bring King Diomedes to the stables, where the mares live. Even though Heracles is said to have unmatched strength, it is a long and reasonably even match, since Diomedes himself is the son of the god of war. He soon loses to Heracles, and is brought to the mares’ manger where they devour him. It is said that this cures them of their hunger for human flesh. It seems that all they longed for was their master’s blood. They become calm and controllable. Heracles is able to bring them back to Tiryns to show Eurystheus his completion of his eighth labour. Eurytheus dedicates the mares to Hera, goddess of marriage, women and childbirth. Once dedicated they were released and free to roam Argos. One of their descendents 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.