George Abramovich Koval (Russian: Жорж (Георгий) Абрамович Коваль, IPA: [ˈʐorʐ (ɡʲɪˈorɡʲɪj) ɐˈbraməvʲɪtɕ kɐˈvalʲ] ^ⓘ, Zhorzh Abramovich Koval; December 25, 1913 – January 31, 2006) was an American engineer who acted as a Soviet intelligence officer for the Soviet atomic bomb project. Koval's infiltration of the Manhattan Project as a GRU (Soviet military intelligence) agent reduced the time it took for the Soviet Union to develop nuclear weapons.

Koval was born in Sioux City, Iowa to Jewish emigrants from the part of the Russian Empire that is now Belarus. As an adult, he traveled with his parents to the Soviet Union to settle in the Jewish Autonomous Region near the Chinese border. Koval was recruited by the GRU, trained, and assigned the code name DELMAR. He returned to the United States in 1940 and was drafted into the U.S. Army in early 1943. Koval worked at atomic research laboratories and, according to the Russian government, relayed back to the Soviet Union information about the production processes and volumes of the polonium, plutonium, and uranium used in American atomic weaponry, and descriptions of the weapon production sites. In 1948, Koval left on a European vacation but never returned to the United States. In 2007, Russian president Vladimir Putin posthumously awarded Koval the Hero of the Russian Federation decoration for his service.

George Koval's father, Abram Koval, left his home town of Telekhany, Russian Empire (now Belarus) to emigrate to the United States in 1910. Abram, a carpenter, settled in Sioux City, Iowa, which, at the turn of the 20th century, was home to a sizeable Jewish community of merchants and craftsmen. Many of these settlers had emigrated from the Russian Empire, in which Jews had been ruthlessly persecuted under the czar's anti-Semitic policies and pogroms. Abram and his wife Ethel Shenitsky Koval raised three sons: Isaya, born 1912; George (or Zhorzh), born 1913; and Gabriel, born 1919.

George Koval attended Central High School, a red-brick Victorian building better known as "the Castle on the Hill". Neighbors recalled that Koval spoke openly of his communist beliefs. While attending Central High he was a member of the Honor Society and the debate team. He graduated in 1929 at age 15. Meanwhile, his parents left Sioux City as the Great Depression deepened. Abram Koval became the secretary for ICOR, the Organization for Jewish Colonization in the Soviet Union. Founded by American Jewish communists in 1924, the group helped to finance and publicize the development of the "Jewish Autonomous Region", the Soviet answer to Jewish emigration to the British Mandate of Palestine then being undertaken by the Zionist movement. The Koval family emigrated in 1932, traveling with a United States family passport. They settled in Birobidzhan, near the border of Manchuria.

The Koval family worked on a collective farm and were profiled by an American communist daily newspaper in New York City. The journalist Paul Novick wrote that the family "had exchanged the uncertainty of life as small storekeepers ... for a worry-free existence for themselves and their children." While Isaya became a tractor driver, George Koval improved his Russian language skills in the collective and began studies at the Mendeleev Institute of Chemical Technology in 1934. At the university, he met and married fellow student Lyudmila Ivanova. Koval graduated with honors in five years and received Soviet citizenship.

At some point Koval was recruited by the Soviet Main Intelligence Directorate (Главное Разведывательное Управление), or GRU. By the time he received his degree he had left Moscow under orders as part of a subterfuge. He was drafted into the Soviet army in 1939 to explain his sudden disappearance from the city. Though his parents had relinquished their US family passport, Koval returned to the US in 1940, replacing a spy recalled during Stalin's purges. His code name was Delmar. Arriving in San Francisco, he traveled to New York City and enrolled at Columbia University. According to Arnold Kramish, an American colleague he befriended and with whom he re-established contact in 2000, it was there that Koval assumed deputy command of the local GRU cell. This outpost operated under the cover of the Raven Electric Company, a supplier to firms such as General Electric. Koval told coworkers he was a native New Yorker and an only child. He ingratiated himself with everyone he met. While Koval originally worked under a pseudonym, gathering information on toxins for use in chemical weapons, his handlers decided to have him work under his real name.

During the beginning of World War II, Congress had re-introduced the draft (conscription) in September 1940, and Koval registered for it on January 2, 1941. Raven Electric Company secured him a year's deferment from service until February 1942. According to historian Vladimir Lota, Koval's handlers wanted him to steal information about chemical weapons and felt that he would not be able to do so while drafted. When the deferment expired, Koval was inducted into the United States Army. He received basic training at Fort Dix in New Jersey before being sent to The Citadel in Charleston, South Carolina. There, Koval served as a private in the 3410th Specialized Training and Reassignment Unit. On August 11, 1943, he was transferred to the Army Specialized Training Program, a unit established in December 1942 to provide talented enlistees with an education and technical training. Koval attended the City College of New York (CCNY) and studied electrical engineering. His CCNY classmates looked up to the older Koval as a role model and father figure who never did homework and was a noted ladies' man, never knowing about his Soviet education and wife. Colleagues recalled that he never discussed politics or the Soviet Union.

The Specialized Training Program was dissolved in early 1944, as the progress of the war tipped in favor of the Allies; many of the CCNY classmates were transferred to the infantry, while Koval and a dozen others were selected for the Special Engineer Detachment. The Detachment was part of the covert project to design, engineer, and fabricate an atomic bomb—an American, Canadian and British initiative known as the Manhattan Project. Koval was assigned to Oak Ridge, Tennessee; at the time, project scientists were researching enriched uranium and plutonium-based bombs, with the Oak Ridge laboratories central to the development of both. The project suffered from a lack of human resources and asked the Army for technically qualified men.