Abdul Qadeer Khan, also known as A.Q. Khan, (born April 1, 1936, Bhopal, India), Pakistani engineer, a key figure in Pakistan’s nuclear weapons program who was also involved for decades in a black market of nuclear technology and know-how whereby uranium-enrichment centrifuges, nuclear warhead designs, missiles, and expertise were sold or traded to Iran, North Korea, Libya, and possibly other countries.

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In 1947, during Khan’s childhood, India achieved independence from Britain, and Muslim areas in the east and west were partitioned to form the state of Pakistan. Khan immigrated to West Pakistan in 1952, and in 1960 he graduated from the University of Karachi with a degree in metallurgy. Over the next decade he pursued graduate studies abroad, first in West Berlin and then in Delft, Netherlands, where in 1967 he received a master’s degree in metallurgy. In 1972 he earned a doctorate in metallurgical engineering from the Catholic University of Leuven in Belgium. Meanwhile, in 1964 he married Hendrina Reterink, a British national who had been born to Dutch expatriate parents in South Africa and raised in what was then Northern Rhodesia (now Zambia) before moving to the Netherlands.

In the spring of 1972 Khan was hired by Physical Dynamics Research Laboratory, a subcontractor of the Dutch partner of URENCO. URENCO, a consortium of British, German, and Dutch companies, was established in 1971 to research and develop uranium enrichment through the use of ultracentrifuges, which are centrifuges that operate at extremely high speeds. Khan was granted a low-level security clearance, but, through lax oversight, he gained access to a full range of information on ultracentrifuge technology and visited the Dutch plant at Almelo many times. One of his jobs was to translate German documents on advanced centrifuges into Dutch.

Khan was heavily influenced by events back home, notably Pakistan’s humiliating defeat in a brief war with India in 1971, the subsequent loss of East Pakistan through the creation of a new independent country, Bangladesh, and India’s test of a nuclear explosive device in May 1974. On September 17, 1974, Khan wrote to Pakistan’s prime minister, Zulfikar Ali Bhutto, offering his assistance in preparing an atomic bomb. In the letter he offered the opinion that the uranium route to the bomb, using centrifuges for enrichment, was better than the plutonium path (already under way in Pakistan), which relied on nuclear reactors and reprocessing.

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Bhutto met Khan in December 1974 and encouraged him to do everything he could to help Pakistan attain the bomb. Over the next year Khan stole drawings of centrifuges and assembled a list of mainly European suppliers where parts could be procured. On December 15, 1975, he left the Netherlands for Pakistan, accompanied by his wife and two daughters and carrying his blueprint copies and suppliers list.

Khan initially worked with the Pakistan Atomic Energy Commission (PAEC), but differences arose with its head, Munir Ahmad Khan. In mid-1976, at Bhutto’s direction, Khan founded the Engineering Research Laboratory, or ERL, for the purpose of developing a uranium-enrichment capability. (In May 1981 the laboratory was renamed the Khan Research Laboratory, or KRL.) Khan’s base of operations was in Kahuta, 50 km (30 miles) southeast of Islamabad; there Khan developed prototype centrifuges based on German designs and used his suppliers list to import essential components from Swiss, Dutch, British, and German companies, among others.

In the early 1980s Pakistan acquired from China the blueprints of a nuclear weapon that used a uranium implosion design that the Chinese had successfully tested in 1966. It is generally believed that the Chinese tested a derivative design for the Pakistanis on May 26, 1990. Khan, having satisfied Pakistan’s needs for its own uranium weapon, began in the mid-1980s to create front companies in Dubayy, Malaysia, and elsewhere, and through these entities he covertly sold or traded centrifuges, components, designs, and expertise in an extensive black-market network. The customers included Iran, which went on to build a uranium-enrichment complex based on the Pakistani model. Khan visited North Korea at least 13 times and is suspected of having transferred enrichment technology to that country. (His laboratory also developed Pakistan’s Ghauri ballistic missile with help from the North Koreans.) Libya, supplied by Khan, embarked upon a nuclear weapons program until it was interrupted by the United States in 2003.

On January 31, 2004, Khan was arrested for transferring nuclear technology to other countries. On February 4 he read a statement on Pakistani television taking full responsibility for his operations and absolving the military and government of any involvement—a claim that many nuclear experts found difficult to believe. The next day he was pardoned by Pakistan’s president, Pervez Musharraf, but he was held under house arrest until 2009. Khan’s critics, particularly in the West, expressed dismay at such lenient treatment of a man whom one observer called “the greatest nuclear proliferator of all time.” For many Pakistanis, however, Khan remains a symbol of pride, a hero whose contribution strengthened Pakistan’s national security against India.