Duke Wilhelm IV of Bavaria enacted The German Beer Purity Law (Reinheitsgebot), strictly regulating beer making.
In English, Reinheitsgebot roughly translates to the German Beer Purity Law, which is a hell of a lot easier to say. Signed by the Bavarian co-rulers Duke Wilhelm IV and Duke Ludwig X into law on April 23rd, 1516, it stipulated that beer, by law, was only to be made with three ingredients: barley, hops, and water.