In the context of espionage or intelligence operations, a "sleeper" refers to an individual who is planted in a target country or organization and remains inactive for an extended period of time until activated to carry out a specific mission.

Sleeper agents are typically recruited by foreign intelligence agencies and trained to blend in with the local population or organization. They may live and work in the target country for years or even decades, maintaining a low profile and avoiding detection.

The goal of a sleeper agent is to remain undetected until they receive orders to carry out their mission, which may include gathering information, sabotaging infrastructure, or carrying out an act of terrorism. Because they have lived in the target country for an extended period of time and have developed a cover identity, sleeper agents can be difficult to identify and apprehend.

The use of sleeper agents is a common tactic in espionage and has been used by many intelligence agencies throughout history. However, the practice is highly controversial and can be seen as a violation of international law and ethics.

The use of sleeper agents has a long history in espionage and intelligence operations. Here are a few examples from history:

Cold War: During the Cold War, both the Soviet Union and the United States used sleeper agents extensively. The Soviet Union's most famous sleeper agent was probably Rudolf Abel, a KGB agent who was arrested in the United States in 1957 and exchanged for American spy plane pilot Francis Gary Powers in 1962. The United States, for its part, ran an extensive program called Operation Solo in the 1950s and 60s, in which FBI agents recruited Communist sympathizers to act as sleeper agents and gather intelligence.

World War II: During World War II, both the Allies and the Axis powers used sleeper agents. One of the most famous examples is Operation Pastorius, a failed German operation to send eight saboteurs to the United States in 1942. The agents, who had been trained in Germany, were intended to destroy key American infrastructure, but were quickly arrested after landing on American soil.

Ancient China: The use of sleeper agents dates back at least to ancient China, where spies were used to gather intelligence and sow discord. The historian Sima Qian recorded a famous example in which the general Sun Bin used a sleeper agent to infiltrate and eventually take over a rival kingdom.

Ancient Greece: The Greeks also made use of sleeper agents, known as "strategoi" or "spies of the general." One famous example is the story of Zopyrus, a Persian general who defected to the Greeks during the Greco-Persian Wars by pretending to be a traitor. Zopyrus was able to convince the Greeks that he was genuinely defecting, and was given a key role in the defense of the city of Babylon. When the Persian army attacked, Zopyrus opened the city gates and allowed the Greeks to capture the city.

These are just a few examples of the use of sleeper agents throughout history. The tactic remains a common one in modern espionage and intelligence operations.