In a 1965 documentary, The Decision to Drop the Bomb, J. Robert Oppenheimer, who had been the scientific director of the American effort to build an atomic bomb during World War II, described his emotions on witnessing the first nuclear detonation. He said, “We knew the world would not be the same. A few people laughed, a few people cried, most people were silent. I remembered the line from the Hindu scripture the Bhagavad Gita. Vishnu is trying to persuade the prince that he should do his duty and to impress him takes on his multiarmed form and says, ‘Now, I am become Death, the destroyer of worlds.’ I suppose we all thought that one way or another.”

It is mesmerizing television. (You can watch the clip on atomicarchive.com.) Oppenheimer–pale, penitent, emaciated, and already elderly at 61–cannot face the camera. He looks down as he speaks. His manner is not tentative–he knows precisely which words he wishes to employ–but painfully subdued. He blinks, he looks away, and at one point he actually seems to wipe away a tear.

This legendary recollection, which today appears in every account of July 16, 1945, may have been theater. His brother Frank, who was at the Trinity test site that day, remembered that Oppenheimer said simply, “It worked.” William Laurence, a New York Times reporter who interviewed Oppenheimer a few hours after the explosion, wrote in his 1959 history, Men and Atoms: The Discovery, the Uses, and the Future of Atomic Energy, that he would never forget the “shattering impact” of the quotation. But Laurence’s initial account, published in the Times in September 1945, has no reference to the Bhagavad Gita. The earliest version of the story occurs in a profile of ­Oppenheimer published by Time magazine in late 1948.

It doesn’t matter. Whether Oppenheimer invented the story of a sudden, vertiginous consciousness of mankind’s new destructive powers or imagined years later that he had thought or said such a thing, the documentary shows a sincerely suffering human being.

Oppenheimer has become a secular saint because he opposed building an early version of the hydrogen bomb when he was chairman of the U.S. Atomic Energy Commission. That opposition led to his persecution by anticommunists and a public hearing to investigate his loyalty, after which his security clearance was permanently revoked because of what were called his “defects” of character. Since his death, biographies have represented him as a cultured leftist intellectual at odds with brutish right-wing militarists. But the physicist’s attitude to the nuclear bomb–and to the capacity of technology to be used for both moral and immoral ends–was more complicated.

In 1965, Oppenheimer told the New York Times Magazine, “I never regretted, and do not regret now, having done my part of the job.” But he also said to Harry ­Truman, “Mr. President, I feel I have blood on my hands.” In truth, he appears to have felt both emotions at once. The nuclear bomb might never have been built without Oppenheimer’s energetic leadership, and he fought hard to see it dropped on civilians at Nagasaki and Hiroshima; but he also thought that its use was mass murder. He justified his role on the grounds that the bomb was necessary to win the war and that it might be a deterrent to future wars, ushering in Immanuel Kant’s era of perpetual peace.

More interesting, Oppenheimer believed that technology and science had their own imperatives, and that whatever could be discovered or done would be discovered and done. “It is a profound and necessary truth,” he told a Canadian audience in 1962, “that the deep things in science are not found because they are useful; they are found because it was possible to find them.” Because he believed that some country would build a nuclear bomb, he preferred that it be the United States, whose politics were imperfect but preferable to those of Nazi Germany or the Soviet Union. When he later opposed building a hydrogen bomb, he was not being inconsistent, nor was he awakening to pacifism late in the day; he opposed an early, infeasible proposal, but he later recanted when the physicist Edward Teller proposed a “technically sweet” design.

Oppenheimer was a fatalist about the evolution of technology and science, which goes some way to explaining his attraction to the deeply fatalistic Gita. Consistent with Vishnu’s teaching to Prince Arjuna, Oppenheimer thought it our duty to perform, as best we can, the jobs that our historical moment allots us. (This aspect of his thinking has been described by the historian James Hijaya in an essay, “The Gita of J. Robert Oppenheimer.”) He looked to humanity’s most progressive institutions to restrain the malignant use of technology. Oppenheimer was asked to build a nuclear bomb, and he hoped reason would dictate that it be used twice, in a just war, and then never again.

Well, so far at least, his ghost must be less troubled than the disturbed figure who appeared in that old documentary. But history lasts a very long time.

Write to me at jason.pontin@technologyreview.com