Saints Cyril and Methodios were brothers from Thessalonica, of distinguished and wealthy parents, Leo and Maria. The elder brother Methodios spent ten years as an officer among the Macedonian Slavs and thus learned the Slavic language. After that, Methodios withdrew to Mount Olympus and dedicated himself to monastic asceticism. It was here that Cyril (Constantine) later joined him. When the king of the Khazars, Kagan, requested preachers of the Christian Faith from Emperor Michael III, these two brothers were found and sent among the Khazars by command of the emperor. Converting King Kagan to the Christian Faith, they baptized him along with a great number of his chief assistants and an even greater number of the people. After some time they returned to Constantinople, where they compiled the Slavonic alphabet consisting of thirty-eight letters. They then proceeded to translate ecclesiastical books from Greek into Slavonic. At the request of Prince Rastislav, they traveled to Moravia, where they spread and confirmed the sacred Faith and made more copies of the books, distributing them to the priests to teach the youth. At the request of the pope, Cyril traveled to Rome. There he became ill and died, on February 14, 867. Then Methodios returned to Moravia and labored to strengthen the Christian Faith among the Slavs until his death. Following his death (he reposed in the Lord on April 6, 885) his disciples, the Five Followers, with St. Clement the bishop at their head, crossed the Danube River and traveled south into Macedonia. There, from Ohrid, they continued their labor among the Slavs, which Cyril and Methodios had begun in the north.
Source: St. Nikolai Velimirovic, The Prologue of Ohrid – Volume One.
Since ye were equal in character to the Apostles, and teachers of the Slavic lands, O divinely-wise Cyril and Methodios, pray to the Lord of all to strengthen all nations in Orthodoxy and unity of thought, to convert and reconcile the world to God, and to save our souls.