Herakles (Hercules) and the Mares of Diomedes

...The eighth labour he enjoined on him was to bring the mares of Diomedes the Thracian to Mycenae.Now this Diomedes was a son of Ares and Cyrene, and he was king of the Bistones, a very warlike Thracian people, and he owned man-eating mares. So Hercules sailed with a band of volunteers, and having overpowered the grooms who were in charge of the mangers, he drove the mares to the sea. When the Bistones in arms came to the rescue, he committed the mares to the guardianship of Abderus, who was a son of Hermes, a native of Opus in Locris, and a minion of Hercules; but the mares killed him by dragging him after them. But Hercules fought against the Bistones, slew Diomedes and compelled the rest to flee. And he founded a city Abdera beside the grave of Abderus who had been done to death. Pseudo-Apollodorus Library 2.5.8 (Loeb) (Perseus Project)

The Labors of Hercules