Diomedes (dī"ōmē'dēz) [key], in Greek legend. 1. Son of Tydeus, he was one of the principal Greek warriors in the Trojan War. Previously he had avenged his father's death in the expedition of the Epigoni against Thebes. 2. A Thracian king, son of Ares and Cyrene. He was killed during the eighth labor of Hercules while trying to protect his man-eating horses. Both also spelled Diomed, Diomede.