He is best known for having invented the Armenian alphabet . That was a basic and important step in strengthening three things : the Armenian Church , the government of the Armenian Kingdom , and connections between the Armenian Kingdom and Armenians living in the Byzantine and Iranian Empires . He is best known for having invented the Armenian alphabet , which was a fundamental step in strengthening the Armenian Church , the government of the Armenian Kingdom , and ultimately the bond between the Armenian Kingdom and Armenians living in the Byzantine Empire and the Persian Empire .