Johannes (Hans) Wilhelm Geiger (September 30, 1882 - September 24, 1945) was a German physicist. Together with Walter Müller he developed the Geiger counter.
In 1902 Geiger began to study physics and mathematics in Erlangen and later attained a doctorate to 1906. In 1907 he began work with Ernest Rutherford in Manchester. Later in Berlin he developed, together with the graduate student Walter Müller, the Geiger counter.