Karl Landsteiner was an Austrian-born American immunologist, physician and pathologist. He was awarded the Nobel Prize in 1930 for Physiology or Medicine for detecting the major blood groups and creating the ABO system of blood typing that revolutionized the process of blood transfusion.
Before him, scientists thought that the blood of every person was the same. Blood transfusion was often considered dangerous. Landsteiner discovered why: when different people’s blood was mixed, the blood cells sometimes clotted.
He announced in 1901, that there were three major human blood groups: A, B and C (which was later called O). One year later in 1902, Landsteiner’s three fellow scientists discovered a fourth blood type named AB. He identified the presence of agglutinins in the blood, and identified, with Alexander S. Wiener, the Rhesus factor, in 1937, thus enabling physicians to transfuse blood without endangering the patient’s life.
Along with his ground-breaking discovery of blood groups, Landsteiner, Constantin Levaditi, and Erwin Popper discovered the polio virus in 1909.
Landsteiner died of a heart attack in 1943.
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