It is not easy to understand the history of the origin of the Cyrillic alphabet. Having preserved the ancient Egyptian papyri, history has left almost no Slavic written monuments to scholars. However, researchers still have some information on this score.
Cyrillic is the symbols used in the alphabets of many Slavic languages, as well as in the languages of the peoples living in the territories of the Slavic states.
Some scholars are inclined to associate the appearance of writing among the Slavs as such with the baptism of Rus in 988, but there are facts refuting this theory. For example, the book "The Legend of the Slavic Writings" by the Bulgarian writer Chernigorizets Hrabra. He proves that the Slavs' written language existed even in the days of paganism, but differed significantly from the present one.
The first creators of a unified, systematized, harmonious writing system were the brothers-educators Cyril and Methodius. The need to create such a writing arose long before the baptism of Rus - at the end of the 9th century. It was necessary to translate Byzantine religious books into a language understandable to the Slavs, so that Christianity could be spread. However, the brothers developed not the Cyrillic alphabet at all, but the Glagolitic alphabet (from the Slavic "to verb" - to speak). This alphabet was based on the Greek alphabet. But the origin of the Cyrillic alphabet itself is still unclear. According to the main theory, it was created by the students and followers of Cyril and Methodius. The Cyrillic alphabet is based on the letters of the Greek alphabet and Glagolitic alphabet. To the 24 letters of the Greek alphabet, 19 more were added to denote sounds that were not used in the Greek language. Most likely, the Cyrillic alphabet was created in Bulgaria. This alphabet got its name in honor of one of the brothers-creators of the Glagolitic alphabet, Cyril.
For more than a thousand years, the Cyrillic alphabet has changed its composition and appearance many times. Most often, these changes were in the nature of simplification - rarely used letters were removed, others acquired a simpler-to-write appearance. Many letters changed their purpose (for example, "ь" and "ъ", which were originally used to denote reduced vowel sounds). But this is in Russian. In the alphabets of other Slavic languages, sometimes there is a neighborhood of Cyrillic and Latin characters, a different spelling of letters from Russian, the presence of characters that are absent in the Russian alphabet.
The form that the Russian alphabet has now, it acquired in 1918, after the decree of the Council of People's Commissars of the RSFSR. Now the Russian Cyrillic alphabet contains 33 letters.