"Double agent" is a counterintelligence term for someone who pretends to spy on a target organization on behalf of a controlling organization, but in fact is loyal to the target organization. Double agents may be agents of the target organization who infiltrate the controlling organization, or may be previously loyal agents of the controlling organization who have been captured and turned by the target; the threat of execution is the most common method of turning a captured agent into a double agent.1 Compare to defector.

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, information to pass along.

The term "double agent" is often used in popular media erroneously to refer to someone acting simply as a spy or secret agent. A spy simply relays information from a target to his or her controlling organization.

A triple agent pretends to be a double agent for the target organization, but in fact is working for the controlling organization all along. Usually, he keeps the trust of the target organization by feeding information to them that apparently is very important but is in fact misleading or useless.

A quadruple agent pretends to be a triple agent for the controlling organization, but actually works for the target organization. Mostly used in fiction and comedy, and rarely known in reality.

List of actual 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. Some, e.g. Mata Hari, may be wrongfully accused innocents.

• Aldrich Ames, worked for CIA and sold information to KGB as a mole
• April Fool
• Joseph Assenza (a.k.a. "Frecks" or "Freckles")
• George Blake
• Guy Burgess, worked for MI5 and gave information to the KGB and later defected
• Mathilde Carré
• John Cairncross, worked at Bletchley Park, gave information to KGB
• Eddie Chapman (a.k.a "ZigZag")
• Roman Czerniawski (a.k.a "Brutus")
• Denis Donaldson
• Kirolos Hanna (a.k.a. Big Papa)
• Moe Gaylus
• Oleg Gordievsky
• Matei Pavel Haiducu
• Robert Hanssen, worked for FBI and sold information to Russia as a mole
• Tyler Kent, sold U.S. secrets before WW2
• Mikel Lejarza
• Katrina Leung, worked for both China and the FBI
• Olivia Mahfouz aka. Gabrella Montez
• Mata Hari (a nickname for her real name)
• Sir Samuel Morland
• Mutt and Jeff
• Arthur Owens (a.k.a "Snow")
• Oleg Penkovskiy (a.k.a "Hero")
• Kim Philby, (Soviet/British) was stripped of his OBE
• Duško Popov (a.k.a "Tricycle")
• Juan Pujol Garcia (a.k.a. "Garbo")
• Freddie Scappaticci (a.k.a "Stakeknife")
• Richard Sorge (a.k.a. "Ramsay")
• Andrew Velocci (a.k.a. "Mandrew")
• Johann Wenzel
• Richard Willis
• Yellow Strom (a nickname for his real name)
• Yoshira