Aspirin's active ingredient (salicylic acid) was originally derived from willow bark, which had been used as a pain reliever since ancient times by Egyptians and Hippocrates. Felix Hoffmann at Bayer chemically synthesized a more stomach-friendly version called acetylsalicylic acid in 1897. Aspirin became the world's first mass-market pharmaceutical and remains one of the most widely taken drugs in history.