He had all-American cover - born in Iowa, college in Manhattan, army buddies with whom he played baseball. George Koval also had a secret. He was a top Soviet spy, code named Delmar, trained by Stalin's ruthless bureau of military intelligence.
Atom spies are old stuff. But historians say Koval, who died last year in Moscow and whose name is just coming to light publicly, appears to have been one of the most important spies of the 20th century.
On Nov. 2, the Kremlin startled Western scholars by announcing that President Vladimir Putin had posthumously given the highest Russian award to a Soviet agent who in World War II had penetrated the Manhattan Project to build the atom bomb.
The announcement hailed Koval as "the only Soviet intelligence officer" to infiltrate the project's secret plants, saying his work "helped speed up considerably the time it took for the Soviet Union to develop an atomic bomb of its own."
Since then, historians, scientists, federal officials and old friends of Koval's have raced to unearth his story - the athlete, the guy everybody liked, the genius at technical studies.
The Soviets were able to turn him, scholars say, because of his Russian Jewish roots.
"He was very friendly, compassionate and very smart. He never did homework," said Arnold Kramish, a retired physicist who studied with Koval at City College and later worked with him on the bomb project.
Stewart Bloom, a senior physicist at the Lawrence Livermore National Laboratory in California, who also studied with Koval, called him a regular guy.
"He played baseball and played it well," usually as shortstop, Bloom recalled. "He didn't have a Russian accent. He spoke fluent English, American English. His credentials were perfect."
Once, Bloom added, "I saw him staring off in the distance and thinking about something else. Now I think I know what it was."
Over the years, scholars and federal agents have identified a half-dozen individuals who spied for the Soviet Union on the bomb project, especially at Los Alamos in New Mexico. All were "walk-ins" - spies by impulse and sympathetic leaning rather than rigorous training.
By contrast, Koval was a mole groomed in Russia by the GRU, the Soviet agency for military intelligence. Moreover, he gained wide access to America's atom plants - a feat unknown for any other Soviet spy. Nuclear experts say the secrets of bomb manufacturing can be more important than those of design.
Los Alamos devised the bomb while its parts and fuel were manufactured at secret plants in places like Oak Ridge, Tennessee, and Dayton, Ohio - sites Koval not only penetrated but also assessed as an army sergeant with wide responsibilities and authority.
"He had access to everything," said Kramish, who worked with Koval at Oak Ridge. "He had his own jeep. Very few of us had our own jeeps. He was clever. He was a trained GRU spy."
That status, he added, made Koval unique in the history of atomic espionage, a judgment historians echo.
Washington has known about Koval's spying since he fled the United States shortly after the war, but kept it secret.
"It would have been highly embarrassing for the U.S. government to have had this divulged," said Robert Norris, author of "Racing for the Bomb," a biography of the project's military leader.
Historians say Putin may have cited Koval's accomplishments as a way to rekindle Russian pride.
"It's very exciting to get this kind of break," said John Earl Haynes, an authority on atomic spying at the Library of Congress. "We know very little about GRU operations in the United States."
The story of how Koval became a spy centers on his Jewish family, which had come from Russia and decided to return.
He was born in 1913 in Sioux City, Iowa, which had a large Jewish community and half a dozen synagogues. In 1932, during the Great Depression, his family immigrated to the Siberian city of Birobidzhan, which Stalin promoted as a secular Jewish homeland.
Henry Srebrnik, a historian at the University of Prince Edward Island who is studying the Kovals for a project on American Jewish communists, said the family belonged to a popular-front organization, as did most American Jews who immigrated to Birobidzhan.
By 1934, Koval was in Moscow excelling in hard studies at the Mendeleev Institute of Chemical Technology. Upon graduating with honors, he was recruited and trained by the GRU and sent back to the United States for nearly a decade of scientific espionage, from roughly 1940 to 1948. How he communicated with his controllers is not publicly known.
In the United States under a false name, he initially gathered information about new toxins, which might find use in chemical weapons. Then his GRU controllers took a gamble and had him work under his own name. Koval was drafted into the army and by chance found himself moving toward the bomb project, then in its infancy.
The army judged him smart and by 1943 sent him for special wartime training in Manhattan at City College. It was famous for Communist radicals, brilliant Jewish students and, after the war, Julius Rosenberg, who was executed for spying for the Soviet Union.
But Koval steered clear of all debate on socialism and Russia, Bloom said.
"He discussed no politics that I can recall. Never," Bloom said. "He never talked about the Soviet Union - never ever, not a word."
At City College, Koval and a dozen or so of his army peers studied electrical engineering.
Meanwhile, the Manhattan Project was suffering severe manpower shortages and asked the army for technically adept recruits. In 1944, Koval and Kramish headed to Oak Ridge, whose main job was to make bomb fuel - considered the hardest part of the atomic endeavor.
Koval gained wide access to the sprawling complex, Kramish said, because "he was assigned to health safety" and drove from building to building making sure stray radiation harmed no workers.
In June 1945, Koval's duties expanded to include top-secret plants near Dayton, said John Shewairy, an Oak Ridge spokesman. The factories refined polonium-210, a highly radioactive material used in initiators to help start the bomb's chain reaction.
In July 1945, the United States tested its first atomic device and a month later dropped two bombs on Japan.
After the war, Koval fled the United States when American counterintelligence agents found Soviet literature hailing the Koval family as happy emigrants from the United States, said a Nov. 3 article in Rossiiskaia Gazeta, a Russian publication.
In 1949, Moscow detonated its first bomb, surprising Washington at the quick loss of what had been an atomic monopoly.
In the early 1950s, Kramish said, the Federal Bureau of Investigation interviewed him and anyone else who had known the spy, asking that the matter be kept confidential.
Bloom at the time was working at the Brookhaven National Laboratory on Long Island. "I was pretty amazed," he recalled. "I didn't figure George to be like that."
In Russia, Koval got his doctorate at his own Mendeleev Institute and taught there for many years, Rossiiskaia Gazeta reported.
His spy role began to emerge publicly in Russia in 2002 with the publication of "The GRU and the Atomic Bomb," a book that referred to Koval only by his code name, Delmar.
Koval reportedly died on Jan. 31, 2006. By American reckoning, he would have been 92, though the Kremlin's statement put his age at 94 and some Russian accounts put it at 93.
Posthumously, Putin named Koval a hero of the Russian Federation, the highest honorary title that can be bestowed on a Russian citizen.