General Discussion

and no reason to doubt corporations anywhere of any size could be involved, as well as academia, government(s), sports, embassies, etc.

Post WWII .... oh, let Google AI tell it:

"Russia issued passports to sleeper agents post-WWII, using them for espionage operations during the Cold War and in later years. These agents, known as "illegals," were trained and deployed in foreign countries to live normal lives while remaining hidden from authorities.

Cold War operations: During the Cold War, Russia's intelligence agencies, such as the KGB and later the SVR and GRU, actively used sleeper agents. These agents were provided with official documents, including passports under false identities, to facilitate their infiltration into Western countries.

Post-Cold War era: Even after the end of the Cold War, Russia continued to use sleeper agents. Intelligence agencies, such as the GRU, have used passports issued under false identities to allow agents to operate and travel internationally. The method of creating false identities sometimes involved obtaining the identities of deceased children, notes The Week."

Also check out:
Russia probably has more undercover 'sleeper' agents who can assassinate Western targets today than during the Cold War
https://www.businessinsider.com/illegals-of-directorate-s-russia-undercover-covert-sleeper-agents-2017-12