A sleeper agent is a person who is trained and prepared to perform a secret mission or task, often for an extended period of time, without any outward indication of their intentions until activated. The term usually refers to someone working on behalf of a foreign government or organization, but can also apply to individuals acting alone or in small groups. Sleeper agents are typically recruited and trained over long periods of time, often years or even decades, before being activated for their mission. They may have no knowledge of their true allegiance until they receive instructions or a trigger event occurs that awakens them to carry out their task.