Life
Pujol's life story begins before WW2. He avoided taking a side in Spain's civil war (although he did ""fight"" for both sides at different times). In Wikipedia's words, "In 1931, Pujol did his six months of compulsory military service in a cavalry unit... He knew he was unsuited for a military career, hating horse-riding and claiming to lack the "essential qualities of loyalty, generosity, and honor"". It was in these years that he developed a healthy distaste for political extremism. He also spent time as a chicken farmer, student, cinema manager, and other things.
But the real story starts with fascists.
The thing was, Juan Pujol Garcia hated fascists, and living in WW2 Spain, that meant he hated his government—a lot. He also hated Hitler, so he approached the British Embassy in Madrid and asked to spy for them. The answer as a resounding "Who the hell are you?" After being refused 3 times—which I honestly can't blame the British for—Pujol decided he needed to be clever about it, so he contacted a German agent in spain This random ex-farmer, who had no background in spywork, made up a fake persona as a fanatically pro-fascist Spanish government official; found someone working for the Nazis; asked to work for them; and was accepted.
The Abweher (German spy service) agent gave Pujol a crash course in espionage, some gear, some money, a code name (Agent ARABAL), and orders to report back from London, as well as to create a network of British agents. Except Pujol never went to London. He went to Lisbon, in Portugal, and began his legacy of utter bullshit.
First of all, Pujol had never left Spain before. As soon as he settled down he started making up reports, based on a tourist's guide to Britain, reference books and magazines from the public library, and newsreels from the cinema. He didn't even understand British currency! He didn't even speak English! But he generated so much information, invented so many fake sub-agents (27, to be exact), that the Germans didn't read into it. They thought this man was a miracle. Suddenly he was their best agent.
It was around this time that the Enigma code was cracked. There wasn't a single real German spy active in England— they were all sitting comfortably in jail, scooped up before they could do any harm. So imagine the surprise of the M16, the British secret service, when they kept hearing about this German agent supposedly in London that still at large. They ordered a full-on spy hunt, and, of course, they found nothing, because Pujol was in Lisbon. But when the mysterious 'Agent ARABAL' sent the German forces on a wild goose chase after a made-up convoy— wasting time and resources— the British realized how valuable this setup could be. (Also that Pujol was full of crap.)
Accounts differ, but the version that makes sense to me is that Pujol next got in contact with American agents. He explains that he's a valuable spy for the Germans but actually intends to double cross them. So America goes to Britain and make an inquiry, and the Embassy remembers that one random dude who wanted to spy for them. M16 realizes it's the same german agent they've been looking for, and Pujol is finally instituted as an actual Allied agent. He's taken to London for real and given the codename Agent GARBO, after actress Greta Garbo. (Cue me laughing because that sounds like Agent Garbage, which is exactly what he fed the Germans. But I digress.)
Set up with a handler, he starts feeding more truth to the Germans, but all of it's either inconsequential or delivered too late to be useful. Remember his 27 fake sub-agents? Every time he makes a mistake he blames one of them. They where also useful because Pujol was reporting so much that the Germans made no further attempts to put agents in London, because he was all they needed. He's sending up to 20 messages a day, over radio now, and it's all lies, and Germany still has no idea!
But then D-Day is coming, the great plan known as Operation Overlord. Pujol becomes heavily involved with Operation Fortitude, which was essentially Operation Pretend Operation Overlord Doesn't Exist and The Allies Are Attacking Not In Normandy. Pujol was absolutely crucial to the Allies' success. His information was heavily valued, as at this point he was the most important of all agents to the Germans; in fact, at one point Hitler got suspicious and began to send troops to Normandy. A lengthy message sent by Pujol to absolutely not do that was sent, and it worked. The troops were turned around and D-Day was carried off. All because the Germans were trusted a Spanish random with the trickery skills of a god. In fact, even after lying about the location of the invasion, Pujol maintained his credibility by sending a message two days before D-Day warning of the real plans. Because snail mail takes so long it was too late to be useful, and it looked like he was really trying to help.
Now to be fair, the Germans weren't just absolute idiots; Pujol had a lot of help. To sell his misinformation, the British literally made fake destroyers, fake airfields with real planes landing on them, inflatable tanks... they went all out to sell the lie. Even before D-Day was coming up, any fake agents or other personnel who "died" in Pujol's reports were given obituaries in the newspaper.
5 months after the storming of Normandy, Pujol was awarded a German medal over radio: the Iron Cross Second Class, which you could only get with personal approval from Hitler himself. The Nazis never uncovered his deception, and a handler gave him the actual medal post-war. To drive in the laughability of this in particular, after the war he was awarded the Member of the Order of the British Empire by the King of England for his service. He is the only person to have high-class medals from both sides of World War 2.
Post-war, appetite for fascist blood sated, Pujol declined the M16's invitation to do more spying, this time on the Soviet Union. Afraid surviving Nazis would come for him— which would be understandable— he faked his death from malaria in Angola, 1949. He moved to Venezuela, divorced his first wife, remarried, and had 3 children, one of whom died before him. For much of the rest of his life ran a bookstore and giftshop. He died in 1988.