Willem J. Kolff was born on 14 February 1911 in Leyden, Holland. His father, Jacob Kolff, was director of the Tuberculosis Sanatorium at Beekbergen, where Kolff spent a great deal of his childhood. Kolff graduated from the Leyden Medical School in 1938, and in 1946 received a Ph.D. summa cum laude from the University of Groningen. During the German occupation of the Netherlands in 1941, he developed the first practical artificial kidney in the ancient town of Kampen, with materials scrounged from a local factory and carefully concealed from the Nazis. In September 1945 the device saved its first patient.