Having inherited a strong and vital state from his predecessors, but defeated in almost all of the wars he waged, Boris I (852-889) made some far-sighted and far-reaching steps, which predetermined Bulgaria's historical fate.
In 864 he converted his court to Christianity and made the Christian religion official in the whole of his kingdom, manoeuvring between the contradictory interests of Rome and Constantinople during the entire period of his reign and achieving various advantages for his country. The momentous affiliation of Bulgaria to the Christian civilization, through its Byzantine model, brought about considerable dividends in her international relations. Moreover, this act catalysed the on-going, and already advanced, process of assimilation of the Proto-Bulgarians by the Slavic majority - a process in which the Bulgarian nationality crystallized: Slavic in its self-identification, language and traditions. In 886, invited by Prince Boris-Michael, the disciples of the Slav apostles Cyril and Methodius, who had been sent away from Greater Moravia by that time, arrived in Bulgaria. They were received with great honours by the Bulgarian governor of Belgrade (Serbia's capital today) as soon as they had reached the border. With the approval of Boris I, two spiritual centres of tremendous significance for Slavic culture were formed in the capital city of Pliska, as well as in the other central town - Ohrid, in Macedonia. Only in Ohrid, in the course of 7 years as many as 3500 students were educated. Steadfastly, Prince Boris I continued his mission. In 893 he summoned a Church Council in Pliska. There "pagan Pliska" was replaced by Veliki Preslav as Bulgaria's capital. The Byzantine priests were sent away, because the country already had well-educated ecclesiastics of her own. And most importantly, at the 893 Council the Bulgarian Slavonic language was declared to be the official administrative and church language. This tongue was comprehensible to the common people. It formed the basis of a cultural tradition that, within a few decades only, overflowed Bulgaria's frontiers and became spread far beyond them. Having accomplished the work of his life, Boris, still in his strength, retired to a monastery. His reign had a cultural impact on the development of all Slavs and the whole of Eastern Europe. He died in 907. However, before finding eternal peace, in 893 he had to prove his loyalty to Christianity once again; in 893 he left the monastery for a while - to dethrone and blind his first-born son Prince Vladimir, who had been conspiring to restore heathendom. After he died, Boris I became the first saint of the Bulgarian Church - the church he himself created. Nowadays, his Proto-Bulgarian, Turkic name, wrongly identified with the Slavonic name of Borislav; is in current usage in almost all countries that belong to the Christian civilization.
Source: Omda.bg