Leo I (pictured), who ruled for nearly 20 years, was crowned Byzantine emperor. Leo I (emperor): Leo I, also known as the Thracian, was Eastern Roman emperor from 457 to 474. He was a native of Dacia Aureliana near historic Thrace. He is sometimes surnamed with the epithet the Great, probably to distinguish him from his young grandson and co-augustus Leo II. February 7, 457. Wiki link