Cyril and Methodius, Saints Cyril, b. c.826, d. Feb. 14, 869, and Methodius, b. c.815, d. Apr. 6, 884, were Greek missionaries and linguists, known as the "Apostles to the Slavs." They were brothers and members of a noble family of Thessaloniki. Cyril was librarian of the church of Hagia Sophia in Constantinople until 860, when he resigned to join Methodius, the abbot of a Greek monastery, in missionary journeys to the Khazars and the Bulgarians.
In 862, Emperor Michael III sent them to Moravia, where they taught and celebrated the liturgy in the Slavonic vernacular, now known as Old Church Slavonic. To translate the Bible into this previously unwritten language, the brothers invented an alphabet based on Greek characters. The Cyrillic alphabet used in modern Slavic languages was attributed to St. Cyril, but it was probably the work of his followers. Cyril died in Rome, where the brothers had gone to defend themselves against German leaders who wanted to enforce the use of the Latin liturgy among the Slavs. Methodius was consecrated an archbishop and returned to Moravia as a papal legate. The German authorities, however, imprisoned (870) him until Pope John VIII secured his release (873). Feast day: May 11 (Eastern); Feb. 14 (Western).
Bibliography: The Apostles of the Slavs (1985); Dittrich, Z. R., Christianity in Great Moravia (1962).
For more information on the Apostles to the Slavs, see the Ukrainian Orthodoxy web site. (This is not an official site of any Orthodox church.)