Karl Landsteiner, ForMemRS (June 14, 1868 – June 26, 1943), was an Austrian biologist and physician. He is noted for having first distinguished the main blood groups in 1900, having developed the modern system of classification of blood groups from his identification of the presence of agglutinins in the blood, and having identified, with Alexander S. Wiener, the Rhesus factor, in 1937, thus enabling physicians to transfuse blood without endangering the patient′s life. With Constantin Levaditi and Erwin Popper, he discovered the polio virus, in 1909. In 1930 he received the Nobel Prize in Physiology or Medicine. He was awarded a Lasker Award in 1946 posthumously and is recognized as the father of transfusion medicine.