Boris I of Bulgaria

Boris I, also known as Boris-Mikhail (Michael) and Bogoris (Bulgarian: Борис I / Борис-Михаил; died 2 May 907), was the ruler of the First Bulgarian Empire in 852–889. At the time of his baptism in 864, Boris was named Michael after his godfather, Emperor Michael III. The historian Steven Runciman called him one of the greatest persons in history.

Despite a number of military setbacks, the reign of Boris I was marked with significant events that shaped Bulgarian and European history. With the Christianization of Bulgaria the traditional state religion Tengriism was abolished. A skilful diplomat, Boris I successfully exploited the conflict between the Patriarchate of Constantinople and the Papacy to secure an autocephalous Bulgarian Church, thus dealing with the nobility's concerns about Byzantine interference in Bulgaria's internal affairs.

When in 885 the disciples of Saints Cyril and Methodius were banished from Great Moravia, Boris I gave them refuge and provided assistance to develop the Bulgarian alphabet and literature. After he abdicated in 889, his eldest son and successor tried to restore the old pagan religion but was deposed by Boris I. During the Council of Preslav which followed that event, the Byzantine clergy was replaced with Bulgarians, and the Greek language was replaced with what is now known as Old Church Slavonic, which in Bulgaria is called and known as Old Bulgarian, as an official language of the Church and the state.