Karl Landsteiner (kärl länt´shtīnər), 1868–1943, American medical research worker, b. Vienna, M.D. Univ. of Vienna, 1891. In 1922 he came to the United States to join the staff of the Rockefeller Institute (now Rockefeller Univ.). He later became a U.S. citizen. For his discovery of human blood groups he won the 1930 Nobel Prize in Physiology or Medicine. As a result of his research in immunology and the chemistry of antigens and serological reactions, he made valuable contributions in hemolysis and in methods of studying poliomyelitis. In 1940 he identified, in collaboration with A. S. Wiener, the Rh factor.