Jordan Carson Mark (July 6, 1913 – March 2, 1997) was a Canadian-American mathematician best known for his work on developing nuclear weapons for the United States at the Los Alamos National Laboratory. Mark joined the Manhattan Project in 1945, and continued to work at Los Alamos under the leadership of Norris Bradbury after World War II ended. He became the leader of the Theoretical Division at the laboratory in 1947, a position he held until 1973. He oversaw the development of new weapons, including the hydrogen bomb in the 1950s. On the hydrogen bomb project he was able to bring together experts like Edward Teller, Stanislaw Ulam and Marshall Holloway despite their personal differences. In July and August 1958, and again the following year, Mark was a scientific adviser to the United States delegation at the Conference of Experts on Detection of Nuclear Explosions. He served on the United States Air Force's Scientific Advisory Board, and its Foreign Weapons Evaluation Group. After he retired from Los Alamos in 1973 he served on the Nuclear Regulatory Commission's Advisory Committee on Reactor Safeguards, and was a consultant for the Nuclear Control Institute. Biography Jordan Carson Mark was born in Lindsay, Ontario, July 6, 1913. He had a brother, James, and five sisters, Margaret, Dorothy, Muriel, Frances and Tony. He received a Bachelor of Arts (BA) degree in mathematics and physics from the University of Western Ontario in 1935, and a Doctor of Philosophy (PhD) in mathematics from the University of Toronto in 1938, writing his thesis "On the Modular Representations of the Group GLH(3,P)" under the supervision of Richard Brauer. Mark taught mathematics at the University of Manitoba, from 1938 until World War II, when he joined the Montreal Laboratory of the National Research Council of Canada in 1943. He came to the Los Alamos Laboratory in May 1945 as part of the British Mission to the Manhattan Project, although he remained a Canadian government employee. He remained at Los Alamos after the war ended, becoming head of its Theoretical Division in 1947, a position he remained in until he retired in 1973. He became a United States citizen in the 1950s. In 1947 the Los Alamos Laboratory, under the leadership of Norris Bradbury, was much smaller than it had been during the war, because most of the wartime staff had returned to their universities and laboratories, but it was still