ボリス1世
For a variety of reasons, Prince Boris I of Bulgaria became interested in converting to Christianity and undertook to do that at the hands of western clergymen to be supplied by King Louis the German of East Francia in 863. Late in the same year, the Byzantine Empire invaded Bulgaria as it suffered famine and natural disasters. Boris was forced to sue for peace. Because the majority of his people were still opposed to Christianity, he was secretly baptized according to the Byzantine rite. The Byzantine Emperor who became his godfather conceded territory in Thrace to him.