The fierce, barbaric king of the Bistones in Thrace, the son of Ares and Cyrene, and husband of Hippodamia. He possessed man-eating mares and he used to throw his guests in the hay-racks for his mares to feed upon (see Mares of Diomedes). Heracles and a band of volunteers overpowered the grooms who were in charge of the mangers, and drove the mares to the coast. When the Bistones overtook them, Heracles entrusted the mares to the guardianship of his friend Abderus, who was eaten up by them. In the ensuing fight Heracles killed Diomedes and threw his body before the mares, and compelled the rest of the Bistones to flee.
- Diodorus Siculus, iv, 15; Servius on Virgil's Aeneid i, 756.
- Pseudo-Apollodorus. The Library ii, 5.8.