Karl Landsteiner won a Nobel Prize for the discovery of what?

Karl Landsteiner (14 June 1868 – 26 June 1943) was an Austrian biologist, physician, and immunologist. He 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.

He identified, with Alexander S. Wiener, the Rhesus factor, in 1937, thus enabling physicians to transfuse blood without endangering the patient's life.

Landsteiner made numerous contributions to both pathological anatomy, histology and immunology, all of which showed, not only his meticulous care in observation and description, but also his biological understanding.

His name will no doubt always be honoured for his discovery of, and outstanding work on, the blood groups, for which he was given the Nobel Prize for Physiology or Medicine in 1930.