The fifth bad guy defeated by Theseus on his way to Athens. Cercyon liked to wrestle people that came by and then kill them. Like Periphetes, some say that he was a son of Poseidon, while others say he was the son Hephaestus. Besides being killed by Theseus, Cercyon is also famous for being horribly mean to his daughter, Alope. More on that story here.