Christian Saints

Two brothers, St. Cyril and St. Methodius, were the founders of the Slavonic liturgy. Their influence spread to part of the southern Slavs, Russians and Bulgarians. At the beginning of the twentieth century, in 1909, there was founded the Sisters of Saints Cyril and Methodius at Danville, Pennsylvania.

St. Cyril
(826-869)
Cyril was born Constantine in Thessalonica around 826, and changed his name only when he became a monk shortly before his death. He had six brothers and sisters, one of them St. Methodius (originally Michael). Their father was an officer in the Legion of Thessalonica and the two brothers spoke the Slavic dialect of Macedonia.
Cyril was 14 when his father died. He moved to Constantinople, where he studied philosophy at the Imperial University. Cyril was ordained priest and then was named librarian at Santa Sophia. Eventually he became a professor at the university. After a mission to the Arabs, he joined his brother, Methodius, who had retired to a monastery on Mount Olympus, in Bythnia.
In 860, they were both sent by Emperor Michael III as missionaries to the partly Christianized Khazars, and in 862 to Moravia, where the duke Rostislav had requested Slavonic-speaking priests. This mision was accepted with enthusiasm. In Moravia, Cyril invented the Glagolithic alphabet (which later produced Cyrillic). Both brothers translated into Slavonic both Biblical and liturgical texts and preached in the vernacular. For this reason they are regarded as the founders of the Slavonic literature.
Thanks to the two brothers, Greek clerical influence increased in Moravia, at the expense of the German clergy who had originally evangelized the country and settled there. Gradually, tension mounted between the two rival priesthoods. The situation was similar in Pannonia. At the end of 867, the rwo brothers left Moravia. They were received with honour in Rome. Cyril, who was seriously ill, took monastic orders and died soon afterwards; he was buried in San Clemente, in Rome.
See: Mikhail Vrubel. St. Cyril.

St. Methodius
(c.815-885)

Methodius was named Archbishop of Pannonia and Moravia the year his brother died (869) and was made Papal Legate to the Slavs. Methodius returned to Pannonia, where he met with resistance from the German bishops. Condemned by a synod held at Regensburg, Methodius was exiled to Ellwangen for 2 years. Pope John VIII released him in 873, but had to forbid the Slavonic liturgy. Finally, however, although Latin was used in the liturgy, the Slav language was not disregarded. Tension between Methodius and the suffragans imposed by Rome was defused only on his death in 885. Methodius died in
 at Velehrad in Czechia in the rank of Archbishop of Moravia.
St. Methodius is regarded as a pioneer of the use of he vernacular in the Liturgy and as a patron of ecumenism.

Pope John Paul II nominated SS. Cyril and Methodius as joint patrons of Europe together with St. Benedict.
Feast day: 11 May in the East; 14 February in the West.
 

Recommended reading:
The Book of Saints: The Lives of the Saints According to the Liturgical Calendar by George Angelini, Victor Hoagland (Editor). Regina Press, Malhame & Company, 1986.
Byzantine Missions Among the Slavs: Ss. Constantine-Cyril and Methodius (Rutgers Byzantine Series) by Francis Dvornik. Rutgers University Press, 1970.
Cyril and Methodius of Thessalonica: The Acculturation of the Slavs by Anthony-Emil N. Tachiaos. St Vladimirs Seminary Pr, 2001.