Robert Bacher (1905-2004) was an American nuclear physicist. Born in Ohio, he received his bachelor's and doctorate in physics from the University of Michigan.
After working at the MIT Radiation Laboratory, Bacher was recruited for the Manhattan Project by J. Robert Oppenheimer. He became head of the experimental physics division at Los Alamos in 1943 and the bomb physics division in 1944 and 1945. Bacher was instrumental in keeping Los Alamos a civilian instead of military laboratory. His wife, Jean, and their two children, Andrew and Martha, also lived at Los Alamos.
Bacher was in charge of G ("Gadget," the bomb's code name) Division, responsible for designing the implosion-type bomb, known as "Fat Man," that was used at Nagasaki. He also helped assemble the plutonium core of the "Gadget" for the Trinity test at the McDonald Ranch House in the New Mexico desert.
He received the Medal of Merit for his work in 1946. After the war, Bacher held a brief position at the United Nations as one of Bernard Baruch's technical advisors, then was appointed to be a charter commissioner on the Atomic Energy Commission (AEC). He later became a member of President Eisenhower's Science Advisory Committee, and was vice president and provost at Caltech.