Avvakum Petrov (Russian: Аввакум Петров; 20 November 1620/1621 – 14 April 1682; also spelled Awakum) was a Russian Old Believer and protopope of the Kazan Cathedral on Red Square who led the opposition to Patriarch Nikon's reforms of the Russian Orthodox Church. His autobiography and letters to the tsar and other Old Believers such as Feodosia Morozova are considered masterpieces of 17th-century Russian literature.