Zeus (also known as Jupiter) is the first Lord of Kobol, from whom all other Lords apparently sprung. He is father to Apollo ("33", "The Hand of God") and, quite likely, to Athena as well (The Hand of God).
When they first meet, Tom Zarek plays on Lee Adama's call-sign, Apollo, by referring to Commander Adama as "Zeus" (Bastille Day). The allusion is repeated in "The Farm", after Zarek has received word that Adama survived Sharon "Boomer" Valerii's assassination attempt.
A Number Three receives a message from Zeus through the oracle Dodona Selloi that "all the Gods weep for you". The oracle then relays a message from the Cylon God to Three regarding the fate of Hera Agathon (Exodus, Part I).