Summarized from René Grousset’s Histoire de l’Armenie.
(Scholarly Preamble: One can observe in Armenian paganism the promiscuous and disorganized nature of polytheism, with gods being adopted in a haphazard and disorganized manner, and their names being changed willy-nilly. This can be contrasted with the linguistically centralized perfection of Islam, in which there is a clear, authorized list of Divine Names with fixed pronunciations and meanings, and in which there is a consistent doctrine of tawhid attached to these names. Considering the Zoroastrian and Hellenic influences on Armenian religion, there must have been some Armenian pagans who were monotheists in the same manner as the Zoroastrians or Platonists.)
Armenian paganism featured a diverse pantheon of deities, some Phrygian, some Iranian, possibly some Urartian, some Assyro-Babylonian, some Syrian, and some Greco-Roman.
I reckon the earliest forms of Armenian paganism must have been predominantly Phrygian, since the Armenian people were originally Thraco-Phrygian. Little is known of the religion of the Phrygians.
One of the Phrygian deities worshipped in ancient Armenia was Ma, the Great Mother, a telluric deity who has been identified with the Cybele of the Greeks. « The Phrygian myth of Cybele-Attis seems to have its equivalent in Armenia with the rock-born deity of mount Diorphus, near the Araxes. »
Armenian pagans practiced sacred slavery or hierodulism, including « sacred prostitution », as was common among the Phrygians.
Armenian religion was heavily influenced by Iranian religion. Hence the use in Armenia of Iranian words like baga (« god ») and yasht (« sacrifice »). The Armenians worshipped Ahura Mazda as Aramazd, the « father of all the gods ». They worshipped Mithra as Mihr. They worshipped the sun as Arev or Areg-akn (« the sun of the eye» aka the visible sun), and the moon as Lusin. They worshipped Tir, the scribe of Aramazd. They worshipped the Iranian god of war Verethragna as Vahagn. Vahagn was known as a Hercules-like figure and a slayer of dragons.
They also worshipped Anahita, an Iranian deity of water and fertility, « the mother of all wisdom », with the name Anaitis. Anahita was celebrated in the month of Navasart with song, dance and flowers. She was revered as Armenia’s special protector.
The Armenian Astlik seems, in Grousset’s estimation, to correspond to the Assyrian Ishtar. She was the goddess of voluptuousness and maternity, and the lover of Vahagn. The Armenian Nane corresponds to various gods of other nations. The Armenian Barcham appears to be derived from the Syrian Baal Shamin.
The Romans (who dominated Armenia and won it over to the West) introduced their gods alongside the existing Armenian gods: « The Olympian Zeus was placed in the temple of Aramazd in Ani, while Athena fraternised with Nane in the temple of Til, and Artemis shared the sanctuary of Erez with Anahita, and Hephaestus was not annoyed to meet the god Mihr in the sanctuary they kept for him at Bagaridj. »
Tir was identified with Apollo and sometimes Hermes. Tir and Mihr and probably some other gods gave their names to several Armenian rulers, notably Tiridate and Mihridate (« gift of Tir », « gift of Mihr »).
Thanks to the Romans, Armenia became Christian.