What has hardly been known is how the Nazis were deluded. It was largely the work of a single man, Juan Pujol Garcia, a Spaniard who fed the Nazis a stream of misleading information from a spy network that existed entirely in his imagination.
Edmon Roch's "Garbo the Spy" is an engrossing documentary that is itself largely a work of the director's imagination. Garcia was code-named "Garbo" because one of his handlers considered him "the greatest actor in the world." Impersonating a man who controlled sources that never existed, he sold the Nazis so convincingly that when he decided one of his spies had to die, the Nazis paid his "widow" a pension.
Based partly on Nigel West's book Operation Garbo: The Personal Story of the Most Successful Spy of World War II, the doc tells the story of an elusive young man from Barcelona who wanted an effect on the war and volunteered his services not once but four times to the British. They eventually accepted him after he had already set up as a free-lancer, feeding his own Nazis contacts information from his fictional network.
Moving to Lisbon, a hotbed of intrigue in Nazi-occupied Europe, he made up most of the information passed on by his "network," and enough of it was true that the Nazis believed him. Over one period of nine months, he even convinced them he was in London. His masterwork was to inform them that the Allies would fake a landing at Normandy to lure the German army there, and then unleash Patton's surprise attack at Calais. They believed him. The fiction worked so well that the Nazis never were up to strength at Normandy, and the fabled Panzer division, while en route there, was diverted to Calais instead.