Sleeper agent

A sleeper agent is a spy or operative who is placed in a target country or organization, not to undertake an immediate mission, but instead to act as a potential asset on short notice if activated in the future. Even if not activated, the "sleeper agent" is still an asset and can still play an active role in sabotage, sedition, espionage, or possibly treason (if enlisted to act against their own country), by virtue of agreeing to act if activated. A team of sleeper agents may be referred to as a sleeper cell, possibly working with others in a clandestine cell system.