'Dead Doubles': FBI Uncovers a Spy Sleeper Cell - Modern Spies - Episode 1 - BBC Two
Putin's Message to Russian "Sleeper Agents" in the West
A sleeper agent is a spy who is placed in a target country or organization not to undertake an immediate mission but to act as a potential asset if activated. Even if unactivated, the "sleeper agent" is still an asset and is still playing an active role in sedition, treason or espionage by virtue of agreeing to act if activated. Sleeper agents are popular plot devices in fiction, particularly in espionage fiction and science fiction. This common use in fiction is directly related to and results from repeated instances of real-life "sleeper agents" participating in spying, espionage, sedition, treason, and assassinations.