Theseus was the son either of Poseidon or Aegeus the king of Athens. His mother was Aethra. The childless Aegeus consulted the Delphic Oracle and was told not to untie his wine skin until he returned home. He did not understand what the oracle meant and so visited his friend King Pittheus of Troezen. Realizing that Aegeus was going to beget a powerful son immediately after the celebration feast for his safe return to Athens, Pittheus made his guest drunk and put him to bed with his daughter Aethra, and so Theseus was conceived. Before he left for home, Aegeus took the pregnant Aethra to a great boulder underneath which he placed his sword and sandals.

He told her that, should she have a son, she must wait until he was strong enough to raise the boulder before she sent him to his father's court. After Aegeus' departure the wily Pittheus said his daughter's lover was really Poseidon. When Theseus came of age, Aethra explained that he was heir to the Athenian throne and he retrieved the sword and sandals. On his journey to Athens he slew several desperate bandits, a fearsome son of Hephaistos, and a dreadful sow, the daughter of the monster Typhon. At Eleusis, then a kingdom separate from Athens, Theseus was forced to accept the challenge of a wrestling match with its king, Cercyon. The aggressive ruler died as a result of the contest, so Theseus became king of Eleusis, which he later added to the Athenian kingdom.

On his arrival in Athens, Theseus learned that his father Aegeus was hardly able to hold on to the throne. Not only was the apparently heir less king challenged by the fifty sons of his half-brother Pallas, but, worse still, Aegeus had fallen under the spell of Medea, the former wife of Jason and a powerful witch. She hoped that her own son Med us would succeed Aegeus. Although Theseus hid his true identity, Medea knew who he was and persuaded Aegeus to let her poison the mighty stranger at a banquet. Theseus was saved when the king recognized his sword as the hero carved the meat. The plot was revealed, Medea fled from Athens with her son, and Aegeus named Theseus as his successor.

The next cycle of Theseus' exploits was designed to secure the safety of Athens. First, he dealt with Pallas's ons. Then he killed a wild bull that was ravaging Marathon, to the north-east of the city. He also overcame the Minotaur, the strange offspring of Pasiphae, the wife of King Minos of Crete. An annual tribute of young Athenians was fed to the Minotaur, which lived in the Labyrinth that had been designed by Daedalus. No one had ever managed to find their way through this maze, so when Theseus volunteered to confront the Minotaur his father despaired.

It was agreed that if Theseus should, by some miracle, survive, he was to change the sail of the tribute ship from black to white on the homeward voyage. At Minos' palace in Knossos the goddess Aphrodite gave Theseus an invaluable ally in Ariadne, a daughter of the Cretan king who fell in love with the hero. Princess Ariadne knew that the Labyrinth was so complex that the only way out was to follow back a thread fastened to the entrance. After Theseus had promised to marry her, Ariadne gave him a ball of thread and a sword. The hero entered the Labyrinth, slew the Minotaur and then set sail for Athens with Ariadne and the rest of the Athenian party. He then left the princess on the nearby island of Dia.

It is thought that he was in love with another woman, but whatever the reason he was soon repaid for his heartlessness. As the ship approached Athens, Theseus forgot to change the sail to indicate to his father that he was alive. Aegeus saw a black sail and, thinking his son dead, threw himself off the Athenian acropolis. The suicide meant that Theseus was now king of Athens, and he joined all the communities of Attica into one state.

Apart from enlarging Athens', Theseus also undertook a number of heroic exploits. On one expedition he captured Hippolyte, the queen of the Amazons, who bore him a son, Hippolytus, but she died shortly afterwards. Theseus gave the accursed Oedipus and his daughter Antigone sanctuary at Colon us, near Athens. But discord entered his own house when his second wife Phaedra, another daughter of Minos, came to desire her stepson Hippolytus, to the young man's horror. Although he promised to keep her passion a secret, Phaedra was so humiliated by his rejection that she hanged herself and left Theseus a letter in which she accused Hippolytus of attempted rape.

He was exiled and died in a chariot accident before his father discovered the truth. In another version, Hippolytus was killed by a sea monster that was raised by Theseus' anger, and Phaedra, filled with remorse, killed herself. Theseus later seized the twelve-year-old Helen, daughter of Zeus, as a future wife. He claimed that only she was worthy enough to be his wife, possibly because of her divine father.

But she had powerful kinsmen, and her two brothers, the Dioscuri, defeated the Athenians and drove Theseus abroad. He died on the island of Scyros, when its king, fearing the presence of such a man, pushed him over a cliff as he admired the view.