Mata Hari - dancer and First World War agent

Margaretha Geertruida Zelle from the Netherlands went down in history as exotic dancer Mata Hari. Due to financial problems, in 1916 she accepted an offer to act as a spy for Germany - an opportunity that came to her thanks to her acquaintance with the German consul to the Netherlands, Karl Cramer. Under the code name H21 she began traveling around the world and seducing generals from the enemy side.

Shortly after that, the head of the French secret service, Georges Ladoux, sent agents to find Mata Hari and offered her work with the French intelligence agency. She was to receive 25,000 francs for every convicted enemy agent.

Mata Hari accepted and became a double agent. However, the French smelled something suspicious. An intercepted telegram from Germany became her downfall. She was tried in a closed hearing on July 24 and 25, 1917, and executed by firing squad on October 15, 1917.

Juan Pujol Garcia - deceiving the Nazis in the Second World War

Spanish-born Juan Pujol Garcia created a false identity as a pro-Nazi Spanish government official and became a convincing German agent during World War II. In reality, he was serving Great Britain under the code name Garbo. The agent - originally trained as a poultry breeder - prepared over 300 bogus reports for the Nazis, who saw him as a reliable source of information.

Garbo successfully led the deception operation intended to mislead the Germans about the location of the Normandy invasion near the end of the war. He made the German officials believe that the D-Day attack by the Allies would take place much further east, near Calais. As a result, three days after the Allies had begun landing in Normandy, the German forces were still focused on defending the area near Calais. Adolf Hitler even stopped two tank divisions heading for Normandy from Calais. This decision proved fatal for the Nazis.

Philby ended up defecting to the Soviet Union

The Cambridge Five - on both sides of the Iron Curtain

The Cambridge Five was a group of spies recruited by the Soviet secret service, KGB, during World War II. It consisted of Kim Philby, Donald Maclean, Guy Burgess and Anthony Blunt, as well as of a suspected but never confirmed fifth member. The group's name refers to the men's recruitment during their education at Cambridge University in the 1930s.

The ring was also connected to the UK's domestic counter-intelligence and security agency, MI5. This allowed the members to put some of their affiliated spies in high-ranking positions within MI5. During World War II, they provided the Soviet Union with information about the Allies' military strategy and later, during the Cold War, they also delivered intelligence. Philby, Burgess and Maclean later defected to the Soviet Union, while Blunt stayed in the UK and became an art professor and a gallery director after being granted immunity from prosecution in exchange for a detailed confession.

Denis Donaldson - Irish terrorist on Britain's side

Hailing from Northern Ireland, Denis Donaldson was an informer for British secret service MI5 in the 1980s and 1990s. At the same time, he was a member of the Provisional Irish Republican Army (IRA) and Irish republican political party Sinn Fein, both of which were not aware of his work for MI5.

Donaldson's double act infuriated Irish nationalists

Donaldson joined the IRA at the age of 16, fighting with the organization, which is classified as a terrorist group, against British rule over Northern Ireland. But the British intelligence service managed to win him over - allegedly by blackmailing him by threatening to expose his promiscuity.

On April 4, 2006, Donaldson was found shot dead in his cottage in County Donegal, Ireland. His work for British intelligence had become public knowledge in 2005. The exact circumstances of his death have never been clarified, with various suspects connected to the IRA and Sinn Fein identified.

Walter Barthel - espionage between East and West Germany

There have been various prominent double agents in German history too. Journalist Walter Barthel started his spying career as an unofficial member of the Stasi, East Germany's state security service. One of his tasks was making contact with a former functionary of the FDJ socialist youth movement who had defected to West Germany, Heinz Lippmann.

Not just a journalist - Walter Barthel

Later, he worked as the editor of West German periodical "Der dritte Weg" (The Third Way), which advocated an alternative to Soviet-style socialism and Western-style capitalism. Its aim was to unite the increasingly weak leftist movement in East Germany with the West German social democratic cause.

Barthel died in 2003, having suffered no consequences as a result of his two-sided government service activities.