Penicillin was discovered by Alexander Fleming in 1928, revolutionizing medicine and marking the advent of antibiotics. Fleming, a Scottish bacteriologist, noticed that a mold called Penicillium notatum had contaminated one of his petri dishes and was killing the surrounding bacteria. This discovery laid the groundwork for the development of penicillin as a treatment for bacterial infections. It became widely used in World War II, significantly reducing morbidity and mortality from infections. Fleming's work opened the door to the discovery of other antibiotics, transforming healthcare by providing powerful tools to combat infectious diseases.