While king, Boris worked aggressively to convert his people to Christianity, even having some nobles executed when they refused to abandon their paganism. He regarded the Christian faith as the crucial civilizing element which would permit the Bulgarians to take their place among the nations of Europe. When the Byzantine and Roman churches competed for the loyalty of the Bulgarian church, he sent the Pope a list of 115 questions and received a famous papal letter in response.
Boris abdicated and entered a monastery in 891. However, in 893, his son and sucessor Vladimir attempted to reestablish paganism. Boris stepped in to depose Vladimir in favor of another son, Simeon, who carried on his work of Christianizing the nation.