Herbert M. Parker (1910-1984) was a British-American medical physicist. He worked at Chicago, Oak Ridge, and Hanford during the Manhattan Project, and is perhaps best known for inventing the rep (a precursor of the rad) and helping develop the rem to measure radiation dosage. 

After earning an M.S. in Physics from the University of Manchester in 1931, Parker worked at Christie Hospital and the Holt Radium Institute in Manchester. Parker moved to Seattle, Washington in 1938, and led radiological physics at the Tumor Institute at the Swedish Hospital. In 1942, Parker joined the Manhattan Project at the University of Chicago as a research associate. The following year, he was assigned to Oak Ridge, where he was responsible for starting the radiological safety program. 

In July of 1944, at the suggestion of Manhattan District Medical director, Robert Stone (he was personally recommended by Arthur Holly Compton) he was asked to organize a radiation protection program in the Medical Department of the Hanford Engineering Works, then operated by the DuPont Company, later by the General Electric Company. Accordingly he headed a section in the Medical Department at Hanford known as Health Instruments and developed a radiation protection program at Hanford, which within a short time became a separate component, the Radiological Sciences Department.

Herbert Parker’s influence on radiation protection, Health Physics, was monumental in that much of the technology developed at Hanford was adopted world wide.  He also personally contributed significantly to the development of radiation protection philosophy and standards, establishing the first maximum permissible concentration for airborne plutonium, as well as developing the concept of physical and biological doses as radiological quantities with their own individual units. Parker received numerous honors and awards for his accomplishments, including election to the National Academy of Engineering in 1978.

Read more at the Atomic Heritage Foundation website