The Armenian Apostolic Church is an Eastern Orthodox Church, the largest Christian denomination in Turkey, and the national church of Armenia. The Church was founded in Armenia, where Christianity was established as the state religion in the year 301 CE. With the fall of the Armenian kingdoms in the 11th century and the rise of the Safavids in Iran in the 16th century, Armenians immigrated to cities throughout Ottoman Empire, particularly in Anatolia and the Levant. In 1742, Rome officially recognized a separate Armenian Catholic Church and over the next two centuries, Protestant and Roman Catholic missionaries proselytized among members of the Armenian Apostolic Church. This led to the official recognition of separate categories for Armenian Apostolic, Armenian Catholic, and Armenian Protestant Christians in the Ottoman millet system.
Like other religious communities, the Armenian Apostolic Church was impacted by Tanzimat Reforms, and lay members created a community constitution in which the patriarchate would henceforth be an elected position. As with all other Armenian groups, members of the Orthodox Church were victims of the Armenian Genocide. The Armenian Apostolic Church is led by Mesrop Mutafyan, the 84th Armenian Patriarch of Constantinople.
Sources:
Bruce Masters, “The Armenian Apostolic Church,” Encyclopedia of the Ottoman Empire, eds. Gabor Agoston and Bruce A. Masters (New York: Facts on File, 2009), pp. 53-54.