How did Theseus die?

skyros killed him by pushing him off a cliff when he was no longer popular in athens.

Edit:

Theseus had fled to the island of Skyros after being declined by his own people because the Athenian's were being told that Theseus was keeping them locked up in the city and took their powers away during Theseus' absence by a noble named, Menestheus.

Theseus died by being pushed off the cliff on the island of Skyros, by the King of Skyros, Lycomedes in fear that Theseus would dethrone him.