Saint Cyril the Philosopher was a 9th-century Byzantine monk, theologian, and missionary born in Thessaloniki. Alongside his brother Methodius, he is famously recognized as one of the Apostles to the Slavs for his extensive work in evangelizing the Early Slavs. He is credited with creating the Glagolitic alphabet, which allowed for the transcription of Old Church Slavonic. After serving as a professor of philosophy, he undertook significant missionary journeys, eventually traveling to Rome, where he died in 869.