Pujol forged documents, invented an identity as a fanatical pro-Nazi Spanish official, and presented himself to German intelligence headquarters. The Abwehr (German military intelligence) welcomed him with open arms.

They gave him £600 (about $42,000 today), taught him the basics of espionage, assigned him the codename "Arabel", and sent him to London to build a spy network.

There was just one problem.

Juan never went to London.

He didn't even speak English.

Instead, he locked himself in a cheap hotel room in Lisbon, Portugal. He bought a tourist guidebook of Britain, a train schedule, a few magazines, and a map.

And from that tiny room, he began constructing the most elaborate lie in military history.

He invented 27 imaginary spies, each with a complete biography, distinct personality, and precise location in Britain. He described the pubs they frequented ( copied from guidebooks ), reported troop movements ( taken from newsreels ), sent weather bulletins. He transmitted detailed military intelligence.

All completely fabricated.

His reports weren't perfect. Once, he told the Germans that on a visit to Glasgow he'd found men who "would do anything for a litre of wine."

( Scots drink whisky. )

He confused currencies and measurements. But every time Berlin questioned him, Juan blamed one of his imaginary informants. According to MI5's official history, the Germans believed him word for word.

By 1942, British intelligence noticed something strange: someone was feeding Germany information from "London"... but no such spy existed.

They traced the source and found Juan still in his Lisbon hotel room, single-handedly running an entire nonexistent spy network with nothing but imagination and a guidebook.

The British recruited him immediately.

They gave him the codename "GARBO", after actress Greta Garbo, because he was "the greatest actor in the world."

They paired him with a brilliant handler named Tomás Harris and brought him to London. What followed would change the course of the war.

From a quiet suburban house, Juan and Tomás wrote 315 letters - averaging 2,000 words each - to a German mail drop in Lisbon. They fed the Nazis a perfect mix of:

• Pure fiction
• True but useless information
• Valuable intelligence that always arrived just a bit too late

When the imaginary agent in Liverpool stopped reporting, Juan told the Germans he had died. He even published a fake obituary in British newspapers.

The Germans were devastated. They sent a pension to the imaginary widow.

According to Warfare History Network, Germany paid Juan $340,000 during the war, nearly $6 million today, to fund a spy network that didn't exist.

But Juan's masterpiece came in 1944.

In the months before D-Day, he sent over 500 messages convincing Germany that the Allied invasion would hit Pas de Calais, not Normandy.

Hours before the Normandy landings on June 6, 1944, Juan sent an "urgent warning" that forces were heading to Normandy beaches.

It arrived too late to help the Germans, but it made Juan look like a genius.

Then, after D-Day, he sent the most important message of all:

On July 29, 1944, Adolf Hitler himself awarded Juan Pujol the Iron Cross, Germany's highest military honor.

Four months later, King George VI awarded him the MBE for services to Britain.

Juan Pujol became one of the only people in history to receive military honors from both sides of World War II, while secretly working against one of them the entire time.

After the war, fearing Nazi retribution, Juan did something equally audacious: in 1949, he faked his own death from malaria, complete with death certificate and burial in Angola.

Then he quietly moved to Venezuela, where he taught languages and ran a small bookstore. He lived anonymously for 35 years.

In 1984, a journalist finally tracked him down. That same year, on the 40th anniversary of D-Day, Juan returned to Normandy.

Veterans who had stormed those beaches lined up to shake his hand and thank him personally.

Juan Pujol García died on October 10, 1988, at age 76, in Caracas, Venezuela.

A failed chicken farmer. Rejected three times by British intelligence. No training. No contacts. No qualifications.

Yet he invented 27 people who never existed, deceived Adolf Hitler into awarding him Germany's highest honor, altered the course of D-Day, and saved tens of thousands of Allied lives.

All from a hotel room with a travel guide and audacity.