Simeon I of Bulgaria

Simeon ruled the First Bulgarian Empire from 893 until his death in 927, inheriting a principality and transforming it through relentless campaigns against Byzantines, Magyars, and Serbs. Under his expansion, Bulgaria claimed territory between the Aegean, Adriatic, and Black seas - the largest it would ever be, and the most powerful state in Eastern and Southeast Europe at the time. Halfway through his reign he stopped calling himself prince and took the title of emperor. The newly independent Bulgarian Orthodox Church became the first patriarchate established outside the original five, and at the Preslav Literary School in the 890s scholars developed the Cyrillic alphabet. Bulgarian translations of Christian texts in Glagolitic and Cyrillic spread across the Slavic world, a cultural flowering so broad that later centuries would call it the Golden Age.