Before we get started, we think it is important to instruct you on how to say Klaus's last name.
"The spelling," a fellow German said of Fuchs's name, "sometimes caused people to pronounce it in a somewhat embarrassing way." The solution for English speakers: pronounce it to rhyme with "books." (Quiet Fellow.(11).9)
Got it? Good. Now that's out of the way we can get down to business.
Klaus Fuchs was a German-born physicist who joined the Communist Party because he was impressed with their willingness to speak out against Hitler. After he was brutally beaten by a gang of Nazi thugs, he escaped to England where he earned his PhD in physics. One thing led to another, and he was recruited to work on the atomic bomb for the British. They knew he had been a communist but thought that maybe he'd leave that behind like he had left Germany. They were very wrong.
A quiet guy, Fuchs always struck his co-workers as a bit enigmatic. While working in Britain he was well liked, but people had the sense that he had some great, underlying sadness to him. When he got to Los Alamos he made much the same impression:
After work, Fuchs walked back to his room in Bachelor Dormitory Number 102. The wife of an Italian physicist used to watch him march slowly past their window, his pale, owlish face turned down toward the muddy path. She named him "Poverino"—the pitiful one. (Two Inside.(24).55)
Well, if you have to have a nickname that one isn't too bad, right? Especially when it's such a fitting one. His only real friend was Richard Feynman, who would tease him about being such a Debbie Downer. But despite the fact that he seemed to be a depressed loner, people liked him. Fuchs was a popular choice as a babysitter at Los Alamos, and he eventually opened himself up enough to offer rides into Santa Fe in his beat-up Buick.
The reticence that people were picking up on was for a good reason: The whole time he was working for the British, and then later for the Americans, Fuchs was passing highly classified information to the Soviets. He was a KGB spy, and he was darn good at it…but that doesn't mean that it was easy.
"In the course of this work, I began naturally to form bonds of personal friendship," Fuchs later said. "I had to conceal from them my inner thoughts." The solution, he explained, was to establish two separate compartments in his mind. "One compartment in which I allowed myself to make friendships, to have personal relations, to help people, and to be in all personal ways the kind of man I wanted to be." This is the Fuchs people saw. They sensed there was something more, something beneath the surface. No one guessed it was Fuchs's "second compartment"—the one he used for his secret mission.
"Everyone thought of him as a quiet, industrious man who would do just about anything he could to help our project," Hans Bethe said. "If he was a spy, he played his role beautifully." (Two Inside.(24).60-61)
After the war, when the FBI exerted incredible pressure on Fuchs to confess what he'd done, he eventually came clean. Like Harry Gold, it seems like it was a relief to be able to finally talk openly about what he'd done:
When friends came to visit [him in jail], Fuchs tried to explain how he had divided his brain into two compartments: one for his commitment to Communism, and one for his personal life. His main regret, he said, was that his secret mission had caused him to lie to his friends.
"You don't know what I had done to my own mind," Fuchs said. (Epilogue.1)
Unlike Gold, however, Fuchs got off pretty easy in terms of punishment. Because he was British, and he had given the secrets to an ally, the maximum sentence was fourteen years. He ended up only serving ten years of this maximum sentence, though, and lived a relatively normal life until he died at the age of seventy-six.