Unknown God
The Unknown God or Agnostos Theos (Ancient Greek: Ἄγνωστος Θεός) is a theory by Eduard Norden first published in 1913 that proposes, based on the Christian Apostle Paul's Areopagus speech in Acts 17:23, that in addition to the twelve main gods and the innumerable lesser deities, ancient Greeks worshipped a deity they called "Agnostos Theos", that is: "Unknown God", which Norden called "Un-Greek". In Athens, there was a temple specifically dedicated to that god and very often Athenians would swear "in the name of the Unknown God" (Νὴ τὸν Ἄγνωστον Ne ton Agnoston).Apollodorus, Philostratus and Pausanias wrote about the Unknown God as well. The Unknown God was not so much a specific deity, but a placeholder, for whatever god or gods actually existed but whose name and nature were not revealed to the Athenians or the Hellenized world at large.
Paul at Athens
According to the book of Acts, contained in the Christian New Testament, when the Apostle Paul visited Athens, he saw an altar with an inscription dedicated to that god (possibly connected to the Cylonian affair), and, when invited to speak to the Athenian elite at the Areopagus gave the following speech: