What is "oprichnik"

Oprichnik (, , man aside; plural Oprichniki) was the term given to a member of the Oprichnina, an organization established by Tsar Ivan the Terrible to govern a division of Russia from 1565 to 1572. Some scholars believe that Ivan's second wife, the Circassian Maria Temryukovna, first had the idea of forming the organization. This theory comes from Heinrich von Staden, a German oprichnik. Maria Temryukovna's brother also became a leading oprichnik.

The Oprichniki were required to swear an oath of allegiance:

I swear to be true to the Lord, Grand Prince, and his realm, to the young Grand Princes, and to the Grand Princess, and not to maintain silence about any evil that I may know or have heard or may hear which is being contemplated against the Tsar, his realms, the young princes or the Tsaritsa. I swear also not to eat or drink with the zemschina, and not to have anything in common with them. On this I kiss the cross.