Myths / Heroes / Theseus. The son of either Poseidon or Aegeus and Aethra, Theseus was widely considered the greatest Athenian hero, the king who managed to politically unify Attica under the aegis of Athens. Son of either Aegeus, the king of Athens, or Poseidon, the god of the sea, and Aethra, a princess, Theseus was raised by his mother in ...