Mares of Diomedes

These flesh-eating horses' belonged to Diomedes of Thrace and were captured by Heracles as part of his 8th labor. After Heracles killed Diomedes, he fed him to the horses, which quelled their desire to eat human flesh. They were presented to Eurystheus and evenutally released to roam the wild. Alexander the Great's horse, Bucephalus, is said to be descended from this breed.