Pittheus

Pittheus was the son of Pelops and Hippodamia. His siblings included Atreus and Thyestes among others. He was the father of Aethra and thus grandfather of Theseus, future King of Athens Pittheus ruled over Troezen, a city composed of the towns of Anthea and Hyperea which he combined.

Theseus
The childless King Aegeus of Athens received an oracular prophecy ("Do not loosen the bulging mouth of the wineskin until you have reached the height of Athens, lest you die of grief."), he approached the famously wise Pittheus for help. Pittheus got Aegeus drunk and the Athenian king lay with Aehtra, Pittheus' daughter. Afterwards, Aethra waded out to an island and lay with Poseidon. When it was revealed that Aethra was pregnant, Aegeus returned to Athens but left with her his sandals, shield and sword. He placed them under a rock and told her that when their son was of age, he should retrieve the items and bring them to Athens, where Aegeus would recognize him.

The child of Aethra, Theseus, grew up in Troezen. A legend states that when Heracles finished his 12 labors, he visited Pittheus and lay down the pelt of the Nemean Lion on a couch so that it was in a lifelike position. When the children came in, all except Theseus ran in terror. Theseus took an axe and attempted to attack the pelt. Theseus eventually grew up and returned to Athens, where he was recognized by his father.

After killing the Minotaur, Theseus succeeded his father and sent his own son (Hippolytus), Pittheus' great-grandson, to Troezen to be raised. Hippolytus was killed, however, by Poseidon, on the wishes of Theseus as the king was led to believe that Hippolytus violated his step-mother (Theseus' wife) Phaedra.