The mythical ancestor of the Doric race, who is described as their king and lawgiver at the time when they were yet inhabiting the northern parts of Thessaly. (Pind. Pyth. i. 124, v. 96.) When involved in a war with the Lapithae, he called Heracles to his assistance, and promised him the third part of his territory, if he delivered him of his enemies. The Lapithae were conquered, but Heracles did not take for himself the territory promised to him by Aegimius, and left it in trust to the king who was to preserve it for the sons of Heracles. (Apollod. ii. 7. § 7; Diod. iv. 37.) Aegimius had two sons, Dymas and Pamphylus, who migrated to Peloponnesus and were regarded as the ancestors of two branches of the Doric race (Dymanes and Pamphylians), while the third branch derived its name from Hyllus (Hylleans), the son of Heracles, who had been adopted by Aegimius. (Apollod. ii. 8. § 3; Schol. ad Pind. Pyth. i. 121.) Respecting the connexion between Aegimius and Heracles, see Müller, Dor. i. 35, &c.
There existed in antiquity an epic poem called "Aegimius," of which a few fragments are still extant, and which is sometimes ascribed to Hesiod and sometimes to Cercops of Miletus. (Athen. xi. p. 503; Steph. Byz. s. v. Abantis) The main subject of this poem appears to have been the war of Aegimius and Heracles against the Lapithae.