The Cyrillic alphabet or azbuka is an alphabetic writing system developed in the First Bulgarian Empire during the 10th century AD at the Preslav Literary School. It is used in various languages, past and present, of Eastern Europe and Asia, especially those of Slavic origin, and also non-Slavic languages influenced by Russian.
Its name derives from tradition that it was invented by the two Byzantine Greek brothers, Saints Cyril and Methodius. Cyril was a Greek monk who, with Methodius, brought written language to Christian converts in the mid-9th century (c.860) in what is now Russia. The Cyrillic alphabet is closely based on the Greek alphabet, with about a dozen additional letters invented to represent Slavic sounds not found in Greek.
In Russia, Cyrillic was first written in the early Middle Ages in clear-cut, legible ustav (large letters). Later a succession of cursive forms developed. In the early eighteenth century, under Peter the Great, the forms of letters were simplified and regularized, with some appropriate only to Greek being removed. Further unnecessary letters were expunged in 1918, leaving the alphabet as it is today—still in use in many Slavic Orthodox countries.