Definition
Karl Landsteiner (1868-1943) was an Austrian-American physician and immunologist. He's most famous for discovering human blood groups (A, B, O). This discovery revolutionized blood transfusions, making them much safer. Landsteiner also identified the Rh factor, another critical component of blood typing. His work earned him the Nobel Prize in Physiology or Medicine in 1930. Think of him as the father of modern blood banking. He made donating and receiving blood a safe and reliable practice.