Cyril and Methodius, Byzantine missionaries; missionaries of Christianity; first teachers of Slavs; fathers of Slavonic literature

http://en.wikipedia.org/wiki/Saints_Cyril_and_Methodius
http://encyclopedia2.thefreedictionary.com/Cyril and Methodi...
“Greek missionaries, brothers, called Apostles to the Slavs and fathers of Slavonic literature."

http://stirenaeus.net/vespers_texts/2011/20110511pdf.pdf
Divinely‐wise Cyril, and God‐loving Methodius, apostles and first teachers of the Slavic church

http://www.holytrinityorthodox.com/calendar/los/May/11-02.ht...
First-Teachers and Enlighteners of the Slavic Peoples, the Brothers Cyril and Methodius

http://www.newadvent.org/cathen/06001a.htm
The first teachers of Christianity seem to be collectively spoken of as "the Fathers" (2 Peter 3:4).