Jan Jansky (1873-1921) was a Czech psychiatrist and serologist who worked in a Prague mental institution under Prof. Kuffner. He became fascinated by the problem of safe blood transfusions, which led him to the discovery in 1907, independently of Karl Landsteiner in the USA, of the four blood primary groups. These he labeled I, II, III, and IV, vice the Landsteiner scheme of A, B, AB, and later 0. During World War I, Jansky served in the Austro-Hungarian Army, where he got the opportunity to experiment with transfusions. Following the war, he practised in Prague. He died at 48 years of age of angina pectoris.