great hero of Attic legend, son of Aegeus, king of Athens, and Aethra, daughter of Pittheus, king of Troezen (in Argolis), or of the sea god, Poseidon, and Aethra. Legend relates that Aegeus, being childless, was allowed by Pittheus to have a child (Theseus) by Aethra. When Theseus reached manhood, Aethra sent him to Athens. On the journey he encountered many adventures. At the Isthmus of Corinth he killed Sinis, called the Pine Bender because he killed his victims by tearing them apart between two pine trees. Next Theseus dispatched the Crommyonian sow (or boar). Then from a cliff he flung the wicked Sciron, who had kicked his guests into the sea while they were washing his feet. Later he slew Procrustes, who fitted all comers to his iron bed by hacking or racking them to the right length. In Megara Theseus killed Cercyon, who forced strangers to wrestle with him.

Theseus had promised Aegeus that if he returned successful from Crete, he would hoist a white sail in place of the black sail with which the fatal ship bearing the sacrificial victims to the Minotaur always put to sea. But he forgot his promise; and when Aegeus saw the black sail, he flung himself from the Acropolis and died.

Theseus then united the various Attic communities into a single state and extended the territory of Attica as far as the Isthmus of Corinth. To the Isthmian Games in honour of Melicertes (see Leucothea), he added games in honour of Poseidon. Alone or with Heracles he captured the Amazon princess Antiope (or Hippolyte). As a result the Amazons attacked Athens, and Hippolyte fell fighting on the side of Theseus. By her he had a son, Hippolytus, beloved of Theseus' wife, Phaedra (see Hippolytus). Theseus is also said to have taken part in the Argonautic expedition and the Calydonian boar hunt.

The famous friendship between Theseus and Pirithous, one of the Lapiths, originated when Pirithous drove away some of Theseus' cows. Theseus pursued, but when he caught up with him the two heroes were so filled with admiration for each other that they swore brotherhood. Pirithous later helped Theseus to carry off Helen (q.v.). In exchange, Theseus descended to the lower world with Pirithous to help his friend rescue Persephone, daughter of the goddess Demeter. But they were caught and confined in Hades until Heracles came and released Theseus.

When Theseus returned to Athens, he faced an uprising led by Menestheus, a descendant of Erechtheus, one of the old kings of Athens. Failing to quell the outbreak, Theseus sent his children to Euboea, and after solemnly cursing the Athenians he sailed away to the island of Scyros. But Lycomedes, king of Scyros, killed Theseus by casting him into the sea from the top of a cliff. Later, according to the command of the Delphic oracle, the Athenian general Cimon fetched the bones of Theseus from Scyros and laid them in Attic earth.

Theseus' chief festival, called Theseia, was on the eighth of the month Pyanopsion (October), but the eighth day of every month was also sacred to him.