Abderus (or Abdhros), is the son of Hermes, or of Thromius the Locriana according to others.
He was a favourite of Heracles, and was torn to pieces by the mares of Diomedes, which Heracles had given him to pursue the Bistones. Heracles is said to have built the town of Abdera to honour him.
According to Hyginus, Abderus was a servant of Diomedes, the king of the Thracian Bistones, and was killed by Heracles together with his master and his four men-devouring horses.
Stories of Abderus
Apollodorus, The Library, 2.5.8
The eighth labour he [King Eurystheus] enjoined on him [Hercules] was to bring the mares of Diomedes the Thracian to Mycenae.1 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,2 and bringing the mares he gave them to Eurystheus. But Eurystheus let them go, and they came to Mount Olympus, as it is called, and there they were destroyed by the wild beasts.Apollodorus, The Library, 2.5.8
1 As to the man-eating mares of Diomedes, see Diod. 4.15.3ff.; Philostratus, Im. ii.25; Quintus Smyrnaeus, Posthomerica vi.245ff.; Tzetzes, Chiliades ii.299-308 （who seems to follow Apollodorus, except that he speaks of the animals in the masculine as horses, not mares）; Strab. 7 Fr. 44, 47, ed. A. Meineke; Stephanus Byzantius, s.v. Ἄβδηρα; Hyginus, Fab. 30 （who gives the names of four horses, not mare).
According to Diod. 4.13.4, Herakles killed the Thracian king Diomedes himself by exposing him to his own mares, which devoured him. Further, the historian tells us that when Herakles brought the mares to Eurystheus, the king dedicated them to Hera, and that their descendants existed down to the time of Alexander the Great.
2 Compare Strab. 7 Fr. 44, 47, ed. A. Meineke; Stephanus Byzantius, s.v. Ἄβδηρα; Philostratus, Im. ii.25. From Philostratus we learn that athletic games were celebrated in honour of Abderus. They comprised boxing, wrestling, the pancratium, and all the other usual contests, with the exception of racing—no doubt because Abderus was said to have been killed by horses.
We may compare the rule which excluded horses from the Arician grove, because horses were said to have killed Hippolytus, with whom Virbius, the traditionary founder of the sanctuary, was identified. See Verg. A. 7.761-780; Ovid, Fasti iii.265ff.
When we remember that the Thracian king Lycurgus is said to have been killed by horses in order to restore the fertility of the land see Apollod. 3.5.1, we may conjecture that the tradition of the man-eating mares of Diomedes, another Thracian king who is said to have been killed by horses, points to a custom of human sacrifice performed by means of horses, whether the victim was trampled to death by their hoofs or tied to their tails and rent asunder.
If the sacrifice was offered, as the legend of Lycurgus suggests, for the sake of fertilizing the ground, the reason for thus tearing the victim to pieces may have been to scatter the precious life-giving fragments as widely and as quickly as possible over the barren earth. Compare Adonis, Attis, Osiris ii.97ff. The games at Abdera are alluded to by the poet Machon, quoted by Athenaeus viii.41, p. 349 B