Either Poseidon or Zeus, but its definatly someone high up in the god pantheon.
To the last person, I keep hoping we will meet Theseus at a later date and it will turn out it was Theseus who led the Argonauts to find the golden fleece, the joke being who ever wrote the myths got there names mixed up.
we have met him ,in the series 1 finale. his name is tycon.