Chekist
Noun
Meaning
(historical) An agent of the Cheka, the Soviet Russian secret police from 1917 to 1922, replacing the Okhrana secret police of Tsarist Russia; succeeded by the OGPU and NKVD.
(by extension, metonymically) A national security official of the KGB, FSB or any of the state security intelligence agencies of the Soviet Union or Russian Federation.
Source: en.wiktionary.orgExamples
Also, the term "chekist" often referred to Soviet secret police throughout the Soviet period, despite official name changes over time.
A member of Cheka was called a "chekist".