Aegimius was the Greek mythological ancestor of the Dorians, who is described as their king and lawgiver at the time when they were yet inhabiting the northern parts of Thessaly. He asked Heracles for help in a war against the Lapiths and, in gratitude, offered him one-third of his kingdom. The Lapiths 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, the Heracleidae.