Mata Hari was one of the most notorious spies in history. Born Margaretha Geertruida Zelle in the Netherlands, she began performing in Paris as an exotic dancer in 1905. She instantly won acclaim for her near-naked performances, which were quite risque for the time. By the time World War I had broken out in 1914, she had retired but was blackmailed by the French to use her seductive powers to spy on Crown Prince Wilhelm. Zelle, it seemed, became a double-agent, promising to spy for the Germans, too. The French eventually uncovered her in a sting operation, and a sensational trial unfolded. Zelle was convicted and executed by firing squad. In hindsight, it appears Mata Hari was more a scapegoat of the French failures during the war rather than any damage she had done as a spy. Many historians believe she was more an unfortunate pawn caught in the horrors of war than femme fatale.

Many Americans don't realize that the Red Army actually defeated the Nazis. One of the men responsible for making this happen was Russian spy Richard Sorge. Sorge was of German descent, but an avid Communist who began spying for the Russians in Germany in the 1920s. It wasn't until World War II that his services became invaluable. He lived in Japan posing as a journalist and was able to obtain vital information about the Axis powers. Most crucially, he found out that Japan was not about to attack the Soviets. This allowed them to reallocate troops against Germany and defeat them in the battle of Moscow, a turning point in the war. Sorge was discovered by the Japanese and executed with Stalin never acknowledging him as a spy; however, he was officially recognized by the Soviet Union as a war hero in 1964 and appeared on several stamps.

Aldrich Ames was not a Communist but a greedy, selfish capitalist who became a double agent for the Soviets for personal gain. Ames was a drunk, depressed CIA agent who cheated on his wife and was going through a messy divorce. In 1985, he sold the names of two KGB officers secretly working for the FBI to the Soviets for $50,000. For the next nine years, he continued selling secrets right under the nose of the CIA. It wasn't until a fellow agent noted that in spite of Ames' $60,000 salary, he was able to afford a $50,000 Jaguar, a half-million dollar mansion for which he paid cash, fancy designer suits, and had all of his stained yellow teeth capped. He was eventually arrested in 1994 and convicted of espionage.

Some of the stealthiest spies in history were not human at all. In the 1960s, the CIA had a secret facility at a children's farm called the IQ Zoo in Hot Springs, Arkansas where they ran a covert program training a variety of animals to perform secret missions. This included ravens, spiders, and even domestic cats. Animals learned tricks like depositing microphones or warning of an enemy approaching using conditioning-based training methods. One of the most incredible projects was called "Acoustic Kitty," in which a microphone was implanted in a cat that was trained to move by sonar impulses and listen to human voices. (The CIA has never officially confirmed or denied any of these operations.)

One of the most unusual deceptions of all time was made by Shi Pei Pu, a male Chinese opera singer who became a spy. For twenty years he pretended to be a woman to seduce and steal secrets from a French Ambassador named Bernard Boursicot. During their infrequent sexual trysts, Shi kept his genitals hidden and later managed to convince Boursicot they had a child together (the boy was actually bought on the black market). The pair were convicted of espionage in 1986 but quickly pardoned by the government for their “silly” affair.

Julius and Ethel Rosenberg were part of a spy ring that funneled vital US atomic information to the Soviets, who were racing to build a bomb of their own in the 1940s. The couple was also able to turn Ethel's brother David Greenglass, who was working on the Manhattan Project. The secrets they revealed were said to have sped up the progress of the Soviet arms race by several years. The Rosenbergs, along with co-conspirator Morton Sobell, were tried and convicted of espionage on March 29, 1951, and sentenced to death. (Sobell served 17 years, and Greenglass made a deal to testify against his sister to save his wife.)

A Spanish farmer, Juan Pujol, was perhaps the greatest double agent ever. He had a passionate hatred for Adolph Hitler, but since Spain was neutral in World War II, he had no direct way to fight the Nazis. That's when he dreamed up a scheme to visit Germany and convince the Nazis to take him on as a spy, and then turn over any information to the Allies. Pujol's ploy was a success — both sides eventually recruited him. One of his most significant contributions was with D-Day. He worked in tandem with the MI5 to convince Hitler that the impending Allied invasion at Normandy was going to take place at Calais. Because of this trickery, Hitler held back several panzer divisions and ensured the success of the attack, saving thousands of lives.

One of the most notorious American spies in the Cold War orchestrated mind control experiments on US citizens. In the 1950s and 60s, Sidney Gottlieb was in charge of a secret CIA project called MK-ULTRA and conducted experiments on the possibility of mind control. Gottlieb was a strong advocate for LSD and under his direction, many people were unwittingly dosed with the drug and their reactions observed. One was Army officer Frank Olson, who ended up committing suicide nine days later. The program was exposed in the 1970s, but Gottlieb was exonerated and given a medal of honor. He died at the age of 80 in India, after having retired there.

One of the Third Reich's most notorious spies was Hermann Görtz, who lead a couple of failed missions. The first was in 1936, when he was arrested in Britain after sketches of an air force base were found in a house he was renting; he was jailed for four years and deported back to Germany. Afterward, he devised a scheme to parachute into Ireland and hope to convince the IRA to side with the Nazis. The first part of the plot was successful — he landed in a field in Ireland in 1940 and established contact. However, a raid by the Irish Police uncovered the plot and Görtz went into hiding for 18 months. He was captured and held in Ireland throughout the war. In 1947, when faced with being deported back to Germany to stand trial for war crimes, he took a cyanide pill and died instantly.

Maria “Belle” Boyd was a Southerner who spied on the Union during the American Civil War. Relying on her Southern charm, she infiltrated Union soldier camps and was able to glean valuable information. In one famous episode, she ran on foot to Major General Thomas J. "Stonewall" Jackson's brigade to give him last minute information before an attack. Belle was arrested several times and finally incarcerated in Washington D.C. but never gave up her love for the Confederacy, hanging the Confederate flag in her cell and sending messages to her supporters with a bow and arrow. After her release, she wrote several memoirs and toured the US, marrying twice and dying in poverty in 1900.