I want to know the answer to the following question:
Who was the Duke of Bavaria in 1516?
All the background I'm provided with is that "In 1516, William IV, Duke of Bavaria, adopted the Reinheitsgebot (purity law), perhaps the oldest food-quality regulation still in use in the 21st century, according to which the only allowed ingredients of beer are water, hops and barley-malt.". Is that enough to answer the question?