During the Reign of Akhenaton
He has sometimes been identified with Yuaa(Yuyu) - but this is highly unlikely as Yuaa married Tuaa(Tuyu) when he was 45 and we know that he did not outlive the dynasty - Yuaa died before the end of the reign of Amenhophis III,
the uncle of Ankhespaaton.
The chances that Ankhespaaton had made Ay her co-regent are slight - it seems very probably that Ay married her only so as to take control of the empire - the right of succession passing through the female line.
Ay conducted the sacred 'opening of the mouth ceremony' for Tutankhamon on this was usually performed by the son of the King - as there was no heir Ay as successor, would have performed this ceremony.
He was however of royal blood and could be considered the last true Pharaoh of the eighteenth dynasty if we accept his relationship to Yuaa.
Ay later married Tye (Tey) - but only made her his queen later - possibly after the death of Ankhespaaton.
Under Akhenaton he was a shrewd advisor and he held important offices:
"Divine father" (Father of the God"
Commander of all His Majesty's horses"
"The King's personal Scribe"
Tutenkhamen made him vizier. He was the perfect courtier - he blew with the wind. During Akhenaton's reign he was an adherent to Aton - later to Amon and as such became King of Egypt. It may be noted that he showed tolerance to Aton after his change of allegiance to Amon.
We know that he had connections with Akhmin (may have been born there) and had a chapel dug for the god Min there. He worshipped Min after his coronation and used the God's name in titles.