Sleeper agent A sleeper agent is a spy who is placed in a target country or organization , not to undertake an immediate mission , but rather to act as a potential asset if activated . Sleeper agents are popular plot devices in fiction , in particular espionage fiction and science fiction . Sleeper agents in espionage . In espionage , a sleeper agent is one who has infiltrated into the target country and had ' gone to sleep ' , sometimes for many years . That is , he or she does nothing to communicate with his or her sponsor nor any existing agents , nor to obtain information beyond that in public sources . They can also be referred to as ' deep cover ' agents . They acquire jobs and identities — ideally ones which will prove useful in the future — and attempt to blend into everyday life as normal citizens . Counter - espionage agencies in the target country cannot , in practice , closely watch all of those who might possibly have been recruited some time before . In a sense , the best sleeper agents are those who do not need to be paid by the sponsor as they are able to earn enough money to finance themselves . This avoids any possibly traceable payments from abroad . In such cases , it is possible that the sleeper agent might be successful enough to become what is sometimes termed an ' agent of influence ' . Sleeper agents who have been discovered have often been natives of the target country who moved elsewhere in early life and were co - opted ( perhaps for ideological or ethnic reasons ) before returning to the target country . This is valuable to the sponsor as the sleeper ' s language and other skills can be those of a ' native ' and thus less likely to trigger suspicion . Choosing and inserting sleeper agents has often posed difficulties as it is uncertain which target will be appropriate some years in the future . If the sponsor government ( or its policies ) change after the sleeper has been inserted , the sleeper might be found to have been planted in the wrong target . Fictional sleeper agents . In fiction , particularly science fiction , sleeper agents fall into two categories . The first is an extension of the real world sleeper agent where an enemy agent is substituted for a person already in a trusted position . The second and more common category involve people who have been subjected to mind control techniques , such as drugs , torture , psychological conditioning , implanted devices , and even telepathic manipulation who then are either released , or allowed to escape back to friendly territory . These sleeper agents are then used by enemy forces to spy , to conduct sabotage , to assassinate certain targets , or for other operations the enemy has in mind for them . During these outbreaks , the sleeper agent doesn ' t normally know what he / she is doing . The substitution sleeper agent was often surgically altered to appear as someone else but more recent versions tend toward androids or clones . Or the agent may have been an infiltrator from the start but brainwashed to believe they are the real thing until activation . Activation of the second kind of sleeper is , at least in novels and stories , done by approaching the agent and uttering a long ago memorized password or pass phrase , or by mailing a postcard with a significant picture to the sleeper . Once a sleeper becomes active , counter intelligence agencies can , at least in principle , become aware of the sleeper as intelligence is collected and transmitted , as instructions are passed , and so on . In popular culture . There are a number of examples of sleeper agents found in science fiction and other forms of entertainment . Many times the unveiling of a sleeper agent is an important part of the plot and acts as surprise element and a plot twist . Some examples of sleeper agents include :