[en] The enormous contribution of Rolf M. Sievert to the science of radiation protection in over 40 years is outlined. His main contributions to clinical physics were from 1920 to 1940 and in 1941 he was primarily responsible for developing the first Swedish radiation protection laws. His institute, under his leadership, was in charge of radiation protection problems in Sweden until he retired in 1965. Sievert was not only the leader in radiation protection in his own country, but he was a giant in the world community. His personal character is praised. (U.K.)