Борис I
The early Cyrillic alphabet was developed in the First Bulgarian Empire and later finalized and spread by disciples Kliment and Naum in the Ohrid and Preslav schools of Tsar Boris I of Bulgaria as a simplification of the Glagolitic alphabet which more closely resembled the Greek alphabet. It was developed by the disciples of Saints Cyril and Methodius at the Preslav Literary School at the end of the 9th century.