Aegimius was the Greek mythological ancestor of the Dorians. He asked Heracles for help in a war against the Lapiths and, in gratitude, offered him one_third of his kingdom. Heracles refused and Aegimius instead raised Heracles' son, Hyllas, alongside his own two sons, Dymas and Pamphylus, who both submitted to Hyllas after their father's death. The names of the three Dorian tribes are derived from the three sons of Aegimius: Hylles, Dymanes and Pamphylii.
They withdrew to Thessaly, where Aegimius, the mythical ancestor of the Donians, whom Heracles had assisted in war against the Lapithae, adopted Hyllus and made over to him a third part of his territory.
After the death of Aegimius, his two sons, Pamphilus and Dymas, voluntarily submitted to Hyllus (who was, according to the Donian tradition in Herodotus V. 72, really an Achaean), who thus became ruler of the Dorians, the three branches of that race being named after these three heroes.
Being desirous of reconquening his paternal inheritance, Hyllus consulted the Delphic oracle, which told him to wait for the third fruit, and then enter Peloponnesus by a narrow passage by sea.