sleeper agent
n. countable C1 Advanced
n. a spy who lives a normal life in another country for a long time. They do not do any spying until they are told to start their secret mission.
n. an espionage operative who is placed in a target country or organisation not to conduct immediate operations, but to establish a deep-cover identity for future activation.
The sleeper agent lived as a quiet librarian for ten years.
After living as a suburban father for a decade, the sleeper agent received a coded message to begin his mission.
Intelligence agencies often struggle to identify the sleeper agent because their fabricated persona is indistinguishable from that of a law-abiding citizen with no suspicious connections.
Usage
Typically used in the context of espionage or political thrillers.