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A double agent, commonly abbreviated referral of double secret agent, is a counterintelligence term used to designate an employee of a secret service or organization, whose primary aim is to spy on a different target organization, but who in fact is a member of that same target organization themselves.
Double agentry may be practiced by spies of the target organization who infiltrate the controlling organization, or may result from the turning (switching sides) of previously loyal agents of the controlling organization by the target; the threat of execution is the most common method of turning a captured agent (working for an intelligence service) into a double agent (working for a foreign intelligence service) or a double agent into a re-doubled agent. It is unlike a defector, who is not considered an agent as agents are in place to function for an intelligence service and defectors are not, but some consider that defectors in place are agents until they have defected.
Double agents are often used to transmit disinformation or to identify other agents as part of counter-espionage operations. They are often very trusted by the controlling organization since the target organization will give them true, but useless or even counterproductive, information to pass along.
Double agents 
Some people listed here are not true double agents (as defined above), but rather (single) agents working as a mole within an intelligence organization.
Pre-twentieth century 
- Samuel Morland, seventeenth century Englishman
- Richard Willis, seventeenth century Englishman
- Yoshira, sixteenth century Japanese
- Benedict Arnold
World War I 
- Mata Hari (stage name for Margaretha Geertruida "Grietje" Zelle)
World War II 
- Mathilde Carré, a French resistance agent who turned for the Germans.
- Roman Czerniawski ("Brutus")
- Eddie Chapman ("ZigZag") infiltrated the German Abwehr during World War II whilst feeding intelligence to MI5. He was so trusted by the Germans that he is reportedly the only British citizen to have ever been awarded the Iron Cross.
- Roger Grosjean ("Fido"), a French Air Force pilot who worked for the British
- Christiaan Lindemans ("King Kong") Dutch agent who turned for the Germans
- Arthur Owens ("Snow")
- Dusan Popov ("Tricycle")
- Mutt and Jeff, Norwegians working for the British.
- Juan Pujol Garcia ("Garbo") British double agent in German spy service-awarded both an MBE and an Iron Cross.
- Johann Wenzel, a member of Red Orchestra who, after being unmasked by the Germans, fed false information to the Soviet Union
- William G. Sebold, German agent working for the FBI
Cold War 
- Aldrich Ames, worked for the CIA and worked for the Soviet Union by selling information to the KGB.
- Cambridge Five: British agents working for the Soviets.
- John Cairncross, British agent working for the Soviets; worked at Bletchley Park and gave information to the KGB.
- Anthony Blunt, British agent working for the Soviets.
- Guy Burgess, British agent working for the Soviets; Worked for MI5 and gave information to the KGB, later defected.
- Donald Duart Maclean, British agent working for the Soviets.
- Kim Philby, British agent working for the Soviets.
- George Blake, British agent working for the Soviets.
- Oleg Gordievsky, later defected to the United Kingdom.
- Matei Pavel Haiducu, Romanian secret agent who defected to France.
- Dmitri Polyakov, GRU officer working for the CIA, executed by the Soviets
- Robert Hanssen, worked for the FBI and sold information to the Soviet Union as a mole.
- Oleg Kalugin, longtime head of KGB operations in the United States. Loyal to the CIA. Provided disinformation regarding American involvement in Prague Spring; and also played a role in the establishment of Yeltsin as post-USSR leader. Convicted in absentia in 2002 by Russian authorities, sentenced to 15 years imprisonment; the US refuses to extradite him.
- Oleg Penkovskiy ("Hero")
- Denis Donaldson, infiltrated the Sinn Féin on behalf the British government. He was found dead in his cottage after a Northern Ireland newspaper revealed this.
- Kevin Fulton (real name Peter Keeley), infiltrated the IRA for British Intelligence. He was allegedly betrayed by his employers and nearly sacrificed to cement Stakeknife's cover in the IRA (see below).
- Freddie Scappaticci ("Stakeknife"), infiltrated the IRA for British Intelligence. Allegedly, the British government ordered him to expose Fulton to increase his own standing in the IRA.
- Robert Nairac British Military Intelligence Agent against the IRA-killed 1977
- April Fool, allegedly an American officer who provided false information to Saddam Hussein.
- Iyman Faris, worked for the FBI, but was loyal to Al-Qaeda.
- Mikel Lejarza ("El Lobo"), Spanish agent working for the Basque separatist ETA.
- Katrina Leung, worked for both China and the FBI.
- Ashraf Marwan, an Egyptian businessman and an alleged spy for Israel, or possibly an Egyptian double agent. Managed to become celebrated as a hero in each country for his alleged work against the other.
Re-doubled agent 
A re-doubled agent is an agent who gets caught as a double agent and is forced to mislead the foreign intelligence service.
F. M. Begoum describes the redoubled agent as "one whose duplicity in doubling for another service has been detected by his original sponsor and who has been persuaded to reverse his affections again".
Triple agent 
A triple agent is an agent who works for three intelligence services, but is usually truly loyal to only one of them.
- Henri Déricourt, Secret Intelligence Service agent with the Special Operations Executive who "turned" for the Germans (d. 1962).
Events in which double agents played an important role 
- Babington plot
- Battle of Normandy
- Cold War
- Battle of Lexington
- Vietnam War
- War on Terrorism
- 1973 Yom Kippur War
- Duquesne Spy Ring
See also 
- List of fictional double agents
- Mole (espionage)
- Double Cross System
- Clandestine HUMINT
- Clandestine HUMINT operational techniques
- Begoum, F.M. "Observations on the Double Agent". Central Intelligence Agency. Retrieved January 5, 2010.