"The rep was devised by Herbert M Parker (1910-1984), a renowned British-American physicist 2. He named it after Wilhelm Roentgen, the discoverer of x-rays. Historically it was also known as the parker and the tissue roentgen."
"The rep (an acronym for Roentgen Equivalent Physical) is a legacy unit of absorbed dose. It refers to the dose of ionising radiation absorbed by living tissue before modification by tissue weighting factors. The rep was superseded by the rad and then by the gray 1,3."