The Oprichnik (Russian: «Опричник», IPA: [ɐˈprʲitɕnʲɪk] ⓘ), also translated as The Guardsman, is an opera in 4 acts, 5 scenes, by Pyotr Ilyich Tchaikovsky to his own libretto after the tragedy The Oprichniks (Russian: Опричники) by Ivan Lazhechnikov (1792–1869).

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.