Aegeus was mythical king of Athens who was a grandson (on his father's side) of Erichtonius. His wife was Aithra, princess of Troizen on the Peloponnese. The couple had a son, the hero Theseus, who was also believed to be the son of Poseidon. Later, Aegeus was also to marry the infamous Medea.
After he had ad his wife pregnant in Troizen, he left her and went back to Athens. Before he left, he hid his sword and sandals under a rock, for his son to get when he was old enough to lift the rock. Theseus did so when he had come of age, and then went to Athens, where his father recognized him.
When Theseus set out to defeat the Minotaur on Crete, Aegeus made him promise to set white sails on the way back, so that he would understand if the mission had been successful. Theseus, however, forgot to do so, and when Aegeas saw the ship return with black sails, he committed suicide by throwing himself off a cliff into the sea. From that day, the sea was named after him: the Aegean Sea.