Illegal "rezident"

In espionage, a resident spy is an agent operating within a foreign country for extended periods of time. A base of operations within a foreign country with which a resident spy may liaise is known as a "station" in English and a rezidentura (residency) in Russian parlance. What the U.S. would call a "station chief", the head spy, is known as a rezident in Russian.

In the former Soviet Union and Russian nomenclature, there are two types of resident spies: legal'nye rezidenty (легальные резиденты, legal resident spy) and nelegal'nye rezidenty (нелегальные резиденты, illegal resident spy). In U.S. parlance, the same distinction is between "official cover" and "non-official cover".

A legal resident spy operates in a foreign country under official cover (such as from his country's embassy). He is an official member of the consular staff, such as a commercial, cultural, or military attaché. Thus, he has diplomatic immunity from prosecution and cannot be arrested by the host country if suspected of espionage. The most the host country can do is send him back to his home country as persona non grata.

An illegal resident spy operates under non-official cover and so they cannot claim immunity from prosecution when arrested. They may operate under a false name and have documents making them out to be an actual national or from a different country from the one for which they are spying. Examples of such illegals include Rudolf Abel, who operated in the United States, and Gordon Lonsdale, who was born in Russia, claimed to be Canadian, and operated in Britain. Famous Soviet "illegals" include Richard Sorge,Walter Krivitsky, Alexander Ulanovsky, and Anna Chapman, who was also known as a sleeper agent.

...
Wikipedia