Landsteiner, Karl (1868–1943), an Austrian-American pathologist. He was awarded the 1930 Nobel Prize in physiology or medicine for his discovery and classification of the four primary types of human blood. This discovery eliminated much of the danger connected with blood transfusions. (See Blood, subtitle Blood Transfusion and Blood Types.) In 1908 Landsteiner identified a virus as the cause of poliomyelitis in monkeys. In 1940 he and Alexander S. Weiner discovered the Rh factor in human blood. (See Blood, subtitle The Rh Factor.)

Landsteiner was born in Vienna. He received an M.D. from the University of Vienna in 1891. Landsteiner was professor of pathology there, 1909–19. In 1922 he moved to the United States, where he became a citizen. He was a member of the Rockefeller Institute for Medical Research for about 20 years.