The Oprichnik or The Guardsman (Russian: Опричник, Oprichnik) is an opera in 4 acts, 5 scenes, by Pyotr Ilyich Tchaikovsky (1840–1893) to his own libretto after the tragedy The Oprichniks (Russian: Опричники) by Ivan Lazhechnikov (1792–1869). The subject of the opera is the oprichniks. It is set in Ivan the Terrible's court during the oprichnina times (1565–1573).
Tchaikovsky worked on the opera from February 1870 - March 1872. It includes music from his early opera The Voyevoda (1869). The work is dedicated to the Grand Duke Konstantin Nikolayevich Romanov. It was given its premiere performance at the Mariinsky Theatre in St Petersburg on 24 April 1874, followed by the Moscow premiere on 16 May 1874 at the Bolshoi Theatre.