Herbert M. Parker (13 April 1910, Accrington – 5 March 1984, Richland, Washington) was an English, and American immigrant, medical physicist. He was a pioneer of medical radiation therapy and radiation safety, known for introducing the roentgen equivalent physical (rep), the forerunner of the gray and the rad, and also the roentgen equivalent biological (reb), the forerunner of the rem and the sievert.