Final answer:
St. Cyril developed the Cyrillic alphabet, allowing the Byzantines to bring their religion and culture to the Slavs.
Step-by-step explanation:
St. Cyril, an important Byzantine missionary, developed an alphabet known as the Cyrillic alphabet. This alphabet allowed the Byzantines to bring their religion and culture to the Slavs. The Cyrillic alphabet is still used in many Slavic languages today, including Russian. St. Cyril translated Greek liturgy into Slavonic and used it to teach and convert the Slavic people, particularly in Moravia and Bulgaria.