Karl Landsteiner, an Austrian-American biologist and physician, made groundbreaking contributions to medical science. Immigrating to New York in 1923, Landsteiner distinguished blood groups in 1900, developing the modern classification system. In 1937, he identified the Rhesus factor, revolutionizing blood transfusions. Alongside Levaditi and Popper, he discovered the polio virus in 1909. Awarded the Nobel Prize in Physiology or Medicine in 1930 and posthumously honored with the Lasker Award in 1946, Landsteiner is celebrated as a pioneer in transfusion medicine, leaving an enduring legacy in medical history.