The Cyrillic alphabet (pronounced 'sih-ril-ic') is a native Slavic alphabet. Now it is used to write Russian, Ukrainian, Belarusian, Rusyn, Bulgarian, Macedonian and for most South Slavic languages. It was developed in the First Bulgarian Empire during the 10th century and it was required by the Soviet Union for many non-Slavic languages in the Caucasus, Siberia, Central Asia and in Northern Russia to be written in Cyrillic.
Old Church Slavonic was the original language of the Slavic people. Old Church Slavonic was used for Russian Orthodox Church. In the 9th century, two monks named St. Cyril and Methodius were missionaries in Eastern Europe who preached to the Slavic people by inventing Glagolitic, which was early Cyrillic. It was based mostly on the Greek alphabet, which was the native language of the two monks, although they added some new letters to represent sounds that were in in the Slavonic language and not in Greek.
During the 18th century Nikolay Karamzin (Nee-kol-ay Karam-zeen) added the Э, Й and Ё letters.
In 1708, Peter the Great added lowercase forms to the letters
In 1991, Azerbaijan, Turkmenistan and Uzbekistan decided to drop the Cyrillic script and adopt the Latin script.