Boris Godunov is an opera by Modest Mussorgsky (1839-1881). The work was composed between 1868 and 1873 in Saint Petersburg, Russia. It is Mussorgsky's only completed opera and is considered his masterpiece. Its subjects are the Russian ruler Boris Godunov, who reigned as Tsar (1598 to 1605) during the Time of Troubles, and his nemesis, the False Dmitriy (reigned 1605 to 1606). The Russian-language libretto was written by the composer, and is based on the "dramatic chronicle" Boris Godunov by Aleksandr Pushkin, and, in the Revised Version of 1872, on Nikolay Karamzin's History of the Russian State.
Boris Godunov, among major operas, shares with Giuseppe Verdi's Don Carlos (1867) the distinction of having the most complex creative history and the greatest wealth of alternative material. The composer created two versionsâ€”the Original Version of 1869, which was rejected for production by the Imperial Theatres, and the Revised Version of 1872, which received its first performance in 1874 in Saint Petersburg. These versions constitute two distinct ideological conceptions, not two variations of a single plan.