Sir Alexander Fleming is credited with the discovery of penicillin in 1928. This significant breakthrough occurred when he observed that a mold called Penicillium notatum inhibited the growth of bacteria in his Petri dishes. Fleming's discovery laid the foundation for the development of antibiotics, which revolutionized medicine and significantly reduced the death rate from bacterial infections. The mass production of penicillin during World War II proved vital in treating wounded soldiers, thereby marking a pivotal moment in public health and medicine.