Theseus was the son of King Aegeus and the human Princess Aethra. While he was a child, he believed that he was a son of Poseidon, but he wasn't.
Theseus volunteered to kill the Minotaur, a half human monster that had been born to the wife of King Minos. On arrival in Crete, Theseus and the king's daughter, Ariadne, fell in love. Ariadne gave Theseus a ball of thread so that when he entered the Labyrinth where the Minotaur was imprisoned he would be able to find his way out. Theseus tied one end of the thread to a door post and sought out the Minotaur in his lair. Theseus came to the centre of the Labyrinth and fought the Minotaur, finally stabbing it in the throat.