The Armenian Apostolic Church is the national church of Armenia. Part of Oriental Orthodoxy, it is one of the most ancient Christian institutions. The Kingdom of Armenia was the first state to adopt Christianity as its official religion under the rule of King Tiridates III, of the Arsacid dynasty in the early 4th century. According to tradition, the church originated in the missions of Apostles Bartholomew and Thaddeus of Edessa in the 1st century. St. Gregory the Illuminator was the first official primate of the church. It is sometimes referred to as the Armenian Apostolic Orthodox Church, Armenian Church or Armenian Gregorian Church.

Gregory the Illuminator was the founder and first official head of the Armenian Apostolic Church. He converted Armenia from Zoroastrianism to Christianity in the early fourth century, making Armenia the first state to adopt Christianity as its official religion. He is venerated as a saint in the Armenian Apostolic Church and in some other churches.