Today is the Feast of Ss Cyril and Methodius. The Roman Martyrology entry of April 6th says of them:
In Moravia, the birthday of St. Methodius, bishop and confessor. Together with his brother, the bishop St. Cyril, whose birthday was the 14th of February, he converted many of the Slav races and their rulers to the faith of Christ. Their feast is celebrated on the 7th day of July.The website of Nobility.org has a fitting article on these two holy brothers:
These brothers, the Apostles of the Slavs, were born in Thessalonica, in 827 and 826 respectively. Though belonging to a senatorial family they renounced secular honors and became priests. They were living in a monastery on the Bosphorus, when the Khazars sent to Constantinople for a Christian teacher. Cyril was selected and was accompanied by his brother. They learned the Khazar language and converted many of the people. Soon after the Khazar mission there was a request from the Moravians for a preacher of the Gospel. German missionaries had already labored among them, but without success.
The Moravians wished a teacher who could instruct them and conduct Divine service in the Slavonic tongue. On account of their acquaintance with the language, Cyril and Methodius were chosen for their work. In preparation for it Cyril invented an alphabet and, with the help of Methodius, translated the Gospels and the necessary liturgical books into Slavonic. They went to Moravia in 863, and labored for four and a half years. Despite their success, they were regarded by the Germans with distrust, first because they had come from Constantinople where schism was rife, and again because they held the Church services in the Slavonic language.
On this account the brothers were summoned to Rome by Nicholas I, who died, however, before their arrival. His successor, Adrian II, received them kindly. Convinced of their orthodoxy, he commended their missionary activity, sanctioned the Slavonic Liturgy, and ordained Cyril and Methodius bishops. Cyril, however, was not to return to Moravia. He died in Rome, 4 Feb., 869.
The fruit of Saint Cyril and Saint Methodius led to the conversion of the family of Vratislav I, Duke of Bohemia. Vratislav's son would become St. Wenceslaus of Bohemia. And there were other canonized saints in his family. May the holy example and good works of these two holy brothers bring about many more saints. Kyrie eleison!