The next day, Aegeus, who had been visiting Aethra at Troizen, left for his home city of Athens. As he left, he left sandals and a sword under a large rock; should Aethra bear a male child, she was to send him to Athens to claim his birthright as soon as he was old enough to lift the rock and retrieve the items.
Aethra gave birth to Theseus, who came of age and set off for Athens with the sword and sandals, encountering and defeating six murderous adversaries along the way. When Theseus reached Athens, Medea, the wife of Aegeus, persuaded Aegeus to kill the as of yet unrecognized Theseus by having him attempt to capture the savage Marathonian Bull. Theseus does the unexpected and succeeds, so Medea tells Aegeus to give him poisoned wine. Aegeus recognizes Theseus' sword as he is about to drink and knocks the goblet from his lips at the last second.
According to Plutarch and Philochoros, on the way to Marathon to kill the bull, Theseus encounters a fierce storm and seeks shelter in the hut of an old woman named Hecale. She promises to make a sacrifice to Zeus if Theseus comes back successful. He comes back, finds her dead, and builds a deme in her name. Some time after Theseus return to Athens, trouble stirs and blood flows between the houses of Aegeus in Athens and Minos, his brother in Crete.
War and drought ensues and an oracle demands that recompense be made to Minos. Minos demands that seven maidens and seven youths are to be sacrificed to the Minotaur every nine years. Theseus is among the chosen victims and sails off to Crete, promising to Aegeus that his ship's black flag would be replaced with a white flag if Theseus is victorious. In Crete, Minos molests one of the maidens and Theseus becomes angry and challenges him, boasting of his parentage by Poseidon. Minos, son of Zeus is amused and asks Theseus to prove his heritage by retrieving a ring from the depths of the ocean. Theseus being a son of Poseidon succeeds.
Ariadne, a young woman in Crete already betrothed to Dionysus, falls in love with Theseus and helps him defeat the Minotaur. Ariadne then leaves Crete with Theseus, who abandons her on Dia (at Athena's behest, according to Pherekydes).
In returning to Athens Theseus forgets to switch the black sail with the white one. Aegeus, consequently, watching from afar believes his son is dead and hurls himself into the sea, named the 'Aegean' after him. After Aegeus' death, Theseus must contend against Pallas for the throne. Theseus gets wind of a planned assassination against him and spoils the ambush, killing Pallas and gaining the throne.
Theseus and a good friend of his by the name of Pirithous wanted to marry daughters of Zeus, and begin their quest by abducting Helen. Theseus wins a bet and gets Helen, but must accompany Pirithous to Hades to recover Persephone for him. There is much disagreement here about what happens in Hades, but many traditions say only Theseus makes it back out.
Theseus does two noteworthy patriotic acts to Thebes, accepting Oedipus at Kolonus, and helping Adrastus bury the Seven, fallen in the struggle for the throne of Thebes. Late in his life Theseus loses popularity in Athens and is exiled. He wanders to Scyrus where he is hurled off a cliff by Lycodemes.