The Mares of Diomedes, also called the Mares of Thrace, were four man-eating horses in Greek mythology

Greek mythology

Greek mythology is the body of myths and legends belonging to the ancient Greeks, concerning their gods and heroes, the nature of the world, and the origins and significance of their own cult and ritual practices. They were a part of religion in ancient Greece...

. Magnificent, wild, and uncontrollable, they belonged to the giant Diomedes (not to be confused with Diomedes

Diomedes

Diomedes or Diomed is a hero in Greek mythology, known for his participation in the Trojan War.He was born to Tydeus and Deipyle and later became King of Argos, succeeding his maternal grandfather, Adrastus. In Homer's Iliad Diomedes is regarded alongside Ajax as one of the best warriors of all...

, son of Tydeus

Tydeus

In Greek mythology, Tydeus was an Aeolian hero of the generation before the Trojan War. He was one of the Seven Against Thebes and was mortally wounded by Melanippus before the walls of the city. The goddess Athena had planned to make him immortal but refused after Tydeus in a rage devoured the...

), king 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...

, a 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...

 who 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...

. Bucephalus

Bucephalus

Bucephalus or Bucephalas was Alexander the Great's horse and one of the most famous actual horses of antiquity. Ancient accounts state that Bucephalus died after the Battle of the Hydaspes in 326 BC, in what is now modern Pakistan, and is buried in Jalalpur Sharif outside of Jhelum, Pakistan...

, Alexander the Great's horse was said to be descended from these mares.
After capturing the Cretan bull

Cretan Bull

In Greek mythology, the Cretan Bull was either the bull that carried away Europa or the bull Pasiphaë fell in love with, giving birth to the Minotaur.- Origin :...

, 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...

 was to steal the Mares.