MIT did a very nice write-up on Hans Geiger, inventor of the Geiger Counter. The article is available online here.
Mr. Geiger worked closely with renowned British scientist Ernest Rutherford. Their work together helped build the foundation of understanding we have today on atomic structure and radioactivity.
He later worked in Germany with Walther Mūller to improve the detector design for higher sensitivity. The modern geiger tube, the heart of all true geiger counters, is referred to as a Geiger-Mūller tube (or detector). Some people use Geiger-Mueller, a variant on the spelling of Mūllers name. It is unclear why the variation in spelling occurs. Often the term GM tube is used as an abbreviation.
GM tubes are still the best solution for radiation detection in some circumstances. They are relatively economical, and good sensitivity can be achieved for alpha and beta radiation if the tube is equipped with a mica window. See the “Noble Pancake Radiation Detector.”