St. Cyril was a 9th-century Byzantine scholar and missionary, best known for his role in the spread of Christianity among the Slavic peoples. He, along with his brother St. Methodius, created the Glagolitic alphabet, which was the first alphabet used to transcribe the Old Church Slavonic language. This innovation helped to promote literacy and religious texts in the Slavic regions. Cyril's work laid the foundation for the development of the Cyrillic alphabet, which is still used today in many Slavic languages, including Russian and Bulgarian. He is venerated as a saint in both the Eastern Orthodox and Roman Catholic traditions, celebrated for his contributions to education and culture.