827 – Saint Cyril born in Thessaloniki to a Greek drungarios (a military officer) named Leon and Maria, possibly a Slav from the hinterlands of Thessaloniki. He was a Greek monk, scholar, theologian, and linguist. He is best known today for his work in Christianising the Slavs and, with his brother Saint Methodius, is credited with devising the Glagolithic and rarely also with devising the Cyrillic alphabet.
862 – Prince Rastislav of Great Moravia requested that the Emperor Michael III and the Patriarch Photius send missionaries to evangelize his Slavic subjects. His motives in doing so were probably more influenced by political than religious motives.
863 – Began the task of translating the Bible into the language now known as Old Church Slavonic and travelled to Great Moravia to promote it. They enjoyed considerable success in this endeavour. However, they came into conflict with German ecclesiastics who opposed their efforts to create a specifically Slavic liturgy.
867 – Pope Nicholas I invited the brothers to Rome. Their evangelising mission in Moravia had by this time become the focus of a dispute with Theotmar, the Archbishop of Salzburg and bishop of Passau, who claimed ecclesiastical control of the same territory and wished to see it use the Latin liturgy exclusively.
868 – Fell ill and retired to a monastery.
869 – After fifty days of illness died on the 14th of February. The Translatio asserts that he was made a bishop before his death, but there is little credible evidence for this.
880 – Approved the use of Old Church Slavonic, which says that the alphabet was "invented by Constantine the Philosopher". It is unclear, however, whether Cyril himself was the originator of the eponymous Cyrillic alphabet. More probably, it was invented by later followers of Cyril and Methodius.
1880 – Was canonized as a saint by the eastern Church, with the Roman Catholic Church canonizing him separately along with Methodius. The two brothers are known as the "Apostles of the Slavs" and are still highly regarded by Catholics and Orthodox Christians. Cyril’s feast day is celebrated on every 14th of February of the Catholic Church or every 11th of May for the Orthodox Church.