Who invented aspirin?

The therapeutic properties of willow tree bark have been known for at least 2,400 years, with Hippocrates prescribing it for headaches. Salicylic acid, the active ingredient of aspirin, was first isolated from the bark of the willow tree in 1763 by Edward Stone of Wadham College, University of Oxford. Felix Hoffmann, a chemist at Bayer, is credited with the synthesis of aspirin in 1897, though whether this was of his own initiative or under the direction of Arthur Eichengrün is controversial. Aspirin is one of the most widely used medications in the world with an estimated 40,000 tons of it being consumed each year. In countries where "Aspirin" is a registered trademark owned by Bayer, the generic term is acetylsalicylic acid (ASA). It is on the WHO Model List of Essential Medicines, the most important medications needed in a basic health system. As of 2015 the cost for a typical month of medication in the United States is less than 25 USD.