Wikipedia
In Greek mythology, Pittheus was a son of Pelops, father of Aethra and Henioche, and grandfather of Theseus. He was the King of Troezen, which he had named after his brother Troezen. When Aegeus asked Pittheus for advice as to how to understand an oracle he received in response to his inquiry whether or not he was going to ever have children, Pittheus got him drunk and Aegeus ended up spending the night with Aethra. Aethra had lain with Poseidon earlier that evening, so when Theseus was born he became Aegeus' stepson.
A Troezenian legend of the earliest notable event of Theseus' life is set in the house of Pittheus. After he had finished his labours, Heracles came to visit Pittheus. He laid his lion-skin down on a couch where it sat in a most lifelike fashion. A little while later Theseus, who was seven years old at this time, came into the room with some of his schoolmates. When the other children saw the skin of the Nemean lion, they ran from it in terror, thinking that it was alive. However, Theseus remained in the room, grabbed an axe from a nearby guard, and attacked the lion-skin.
Pittheus also appears in the myth about Hippolytos, son of Theseus and thus Pittheus's great-grandson. When Theseus, now king of Athens, marries Phaedra, he sends Hippolytos to Pittheus, who raises him as heir to the Troezen throne. However, Hippolytos later gets killed by Poseidon when his father is led to believe he violated Phaedra and caused her to commit suicide.