Cyrillic

From Slavic.info

The Slavs influenced by the Greek faith have what is called the Cyrillic alphabet.

Cyril was a Greek monk, who went from Constantinople (a. D., 862), to preach the gospel to the Slavs.

The alphabet called Cyrillic, thought to have been invented by Cyril, is today known as Glagolitic.

This alphabet was later replaced by adaptations of the uncial Greek alphabet, with the addition of a number of new letters to express sounds not found in the Greek language. It is this alphabet which is now known as Cyrillic.