On June 6, 1984, on the 40th anniversary of the D-Day landings, a 72-year-old man toured Normandy's beaches to pay his respects to the troops who gave their lives spearheading the invasion that would become instrumental in bringing about Hitler's downfall.

The man was not a former soldier. He had been neither a military nor a government official for the Allies, and he had no connection with this part of northern France. In fact, the man was a failed poultry farmer who had been born in Barcelona in 1912.

Thirty-five years later, Thursday sees the 75th anniversary of D-Day, but while the world commemorates the invasion that turned the tide of the Second World War, few will be aware that Operation Overlord was a success thanks to the efforts of a Catalan called Joan Pujol.

Double agent

In fact, the reason Pujol was in Normandy 35 years ago, four years before his death, was part of the recognition the British authorities finally awarded him for his spying work as a double agent deceiving Nazi Germany about the Allies' true intentions in 1944.

Pujol is better known by his codename "Garbo," after the famous Hollywood starlet of the time Greta Garbo (he was "Alaric" to his German handlers), but when he first offered his spying services to British military intelligence he was turned down, three times.

Undeterred, Pujol won over the Germans instead, posing as a zealous pro-Nazi Spanish government official based in Lisbon, where he invented a network of fictitious agents in Britain feeding fake information to Germany that entirely conned the Nazi authorities.

The success of his misinformation campaign finally convinced British intelligence to take him on and Garbo moved to the UK and continued with his efforts at misleading the Germans along with his handler, the Spanish-speaking Tomás Harris.

Iron Cross and MBE

So successful was Garbo's manipulation of both fake and real information that the Germans ended up financing a network of 27 fictitious agents, and even stopped recruiting spies in the UK. In fact, Pujol was awarded the Iron Cross for his "services" to the German war effort.

Yet, Pujol was no true friend to the Nazi regime. A consequence of his experiences in the Spanish Civil War was that he developed an abiding distaste for both communism and fascism, leading him to volunteer to serve the British, the only one of their spies to do so.

For his effectiveness and loyalty, the British made Garbo a Member of the Order of the British Empire (MBE), and when the Allies began preparing for D-Day, which would see an invasion force of 160,000 landing in Normandy, they turned to Pujol for help.

Operation Fortitude

While the Germans had got wind of the plans for Operation Overlord being commemorated this week, Garbo distracted them with Operation Fortitude, a deception campaign in which the Catalan spy convinced the Nazis that the main attack would be at Pas de Calais.

Garbo got to work, sending the Germans over 500 radio messages between January 1944 and D-Day. That split the German forces and prevented them from reinforcing their defences in Normandy where the actual invasion was set to take place.

The D-Day landings were vital for the success of Operation Overlord and Garbo's manipulation of the Germans played a major role, not only in ensuring the Allies took back western Europe, but that the figure of 120,000 Allied casualties was not much higher.

Refuge in Venezuela

After the war, Garbo avoided Nazi reprisals by faking his death and moving to Venezuela, where he ran a small business. It was only thanks to detective work done by a former British politician and writer, Rupert Allason, that the world was reacquainted with this unlikely hero.

In 1984, Pujol was received by Prince Philip at Buckingham Palace and was reunited with former British intelligence officers he had worked with during the war. He died four years later in Caracas and was buried in the town of Choroní, next to the Caribbean Sea.

Pujol's legend lived on and his story was told in a 2009 film called Garbo: The Spy. As the world commemorates the efforts of thousands of soldiers on Thursday, one hopes a thought will be spared for a Barcelona poultry farmer who was key in bringing down Hitler's regime.