Since its creation, the Cyrillic alphabet has adapted to changes in spoken language and developed regional variations to suit the features of national languages. It has been the subject of academic reforms and political decrees. The form of the Russian alphabet underwent a change when Tsar Peter I of Russia introduced the Civil Script in 1708. Some letters and breathing marks, which were only used for historical reasons, were dropped. Medieval letterforms used in typesetting were harmonized with Latin typesetting practices. The old Cyrillic letter names, however, remained until XIX when they were simplified and replaced by the modern ones.
By the way, the Russian word for alphabet, azbuka, is made of the old names of the first two letters of the Cyrillic alphabet, Az and Buki.