Though less famous (or notorious) than some of his peers, John Fitzgerald Byers called him probably "the most evil" Nazi to be offered asylum. During World War II, he experimented on Jewish concentration camp inmates, his particular interest being the effects of water or extremes of pressure on the human body. To this end, his many "subjects" were drowned, suffocated, and placed in decompression chambers.
Offered asylum in the U.S., his scientific knowledge was applied to researching the effects of high-altitude flight on human bodies, advancing the U.S. space program enough to put astronauts on the moon before the Soviet Union.
He was later employed by the Syndicate as a biologist trying to create an alien human hybrid. The degree to which he succeeded is not clear, but he was given a generous retirement at the expense of the U.S. Government. His hobby, appropriately, was the breeding of orchids.
Confronted by Fox Mulder and Dana Scully in his home, he remained cagey about the exact nature of his work, but offered them a few clues to help them on their way. He expressed some remorse for his past actions - though it seemed that he did not regret the lives he had taken as much as the fact that he would never be remembered as a great scientist.
Klemper is likely modeled on Hubertus Strughold, a Nazi scientist who came to the U.S. after the war and was instrumental as the "Father of Space Medicine," a legacy subsequently tarnished by evidence of his wartime experiments on inmates of the Dachau concentration camp. His name is given to the fictional Strughold Mining Company that appears in "The Blessing Way," and to the fictional character Conrad Strughold.