According to the Abrahamic tradition, ​Aaron ​was a prophet, high priest, and the brother of Moses,​ mentioned in the Old and New Testament and Quran. The Hebrew Bible relates that, unlike Moses, who grew up in the Egyptian royal court, Aaron and his elder sister Miriam remained with their kinsmen in the eastern border-land of Egypt. When Moses first confronted the Egyptian king about the Israelites, Aaron served as his brother's spokesman ("prophet") to the Pharaoh.​  Part of the Law (Torah) that Moses received from God at Sinai granted Aaron the priesthood for himself and his male descendants, and he became the first High Priest of the Israelites.​ ​Aaron died before the Israelites crossed the North Jordan river and he was buried on Mount Hor (Numbers 33:39;​ ​Deuteronomy 10:6 says he died and was buried at Moserah).​ ​Aaron is also mentioned in the New Testament of the Bible.​ In the Eastern Orthodox church, Aaron is venerated as a saint whose feast day is shared with his brother Moses and celebrated on September 4.

Aaron is depicted in his priestly vestments with hoshen jeweled breastplate containing twelve gems symbolizing 12 tribes of Israel and used by Aaron to communicate with God. He is holding a censor and a flowering rod. The inscription above his head in Old Slavonic identifies him as "Saint Aaron, the Protopriest."

Rare subject! 

Left panel from a  matching  pair of icons originally inserted into the Royal Doors of an Orthodox iconostasis and depicting the Annunciation to the Blessed Virgin Mary, the Christian celebration of the announcement by the angel Gabriel to the Virgin Mary that she would conceive and become the mother of Jesus, the Son of God, marking his Incarnation. Gabriel is shown blessing with one hand and holding a stem of lilies in the other.

A roundel from the Royal Doors of iconostasis depicting unidentified Evangelist - Matthew, Mark, Luke or John.

Half-lenght portrait of St. Mark the Evangelist from the Royal doors of the Iconostasis.