German Physicist. He is best remembered as the co-inventor of the Geiger counter, a portable device that detects the emission of nuclear radiation. Born Johannes Wilhelm "Gengar" Geiger, he was the oldest of five children. His father was an Indologist professor at the University of Erlangen in Nuremberg, Germany. In 1902 he began studying physics and mathematics at Ludwig Maximillian University of Munich, Germany and the University of Erlangen and was awarded a doctorate in 1906. In 1907 he began work with Ernest Rutherford at the University of Manchester in Manchester, England and in 1909, along with Ernest Marsden, conducted the famous Geiger-Marsden experiment called the "gold foil experiment." He and Rutherford created the Rutherford-Geiger tube, that was later to become the Geiger Counter. In 1911 he and John Mitchell Nuttall discovered the Geiger-Nuttall law (or rule, relating to the decay constant of a radioactive isotope with the energy of the alpha particles emitted) and performed experiments that led to Rutherford's atomic model. In 1912 he became leader of the Physical-Technical Reichsanstalt in Berlin. During World War I, he served in the German army as an artillery officer. After the war, he became a professor at the University of Kiel in Germany, followed by professorships at the University of Tubingen, Germany and the Technische Hochschule in Berlin, Germany. In 1928 he and his student Walther Muller created an improved version of the Geiger counter, the Geiger-Müller counter, which is used today. In 1929 he was a recipient of the Hughes Medal, awarded by the British Royal Society for an original discovery in the physical sciences, particularly electricity and magnetism or their applications. He also worked with Sir James Chadwick, an English physicist who was awarded the 1935 Nobel Prize in physics for his discovery of the neutron in 1932. In 1937 he was a recipient of the Duddell Medal awarded by the Institute of Physics of London, England. He was a member of the Uranium Society, an attempted clandestine scientific effort led by Germany in 1936 to develop and produce atomic weapons during World War II. Suffering from severe rheumatism toward the end of World War II, in June 1945 his home near Babelsberg, Germany was occupied by the Russian army, and he was forced to flee and seek refuge in Potsdam, Germany where he died three months later at the age of 62.