Alexander Fleming is credited with discovering penicillin in 1928. This groundbreaking antibiotic was found accidentally when Fleming noticed that a mold, later identified as Penicillium notatum, had contaminated one of his petri dishes and was inhibiting the growth of bacteria. His discovery revolutionized medicine, providing a powerful means to treat bacterial infections that were previously life-threatening. Penicillin marked the beginning of antibiotics, transforming healthcare and significantly reducing mortality rates associated with infectious diseases. Fleming's work earned him the Nobel Prize in Physiology or Medicine in 1945, acknowledging the profound impact of his discovery on modern medicine.