Penicillin (1928)

Alexander Fleming's accidental discovery of penicillin in 1928, and Howard Florey and Ernst Chain's development of it as a usable antibiotic in 1940, saved an estimated 200 million lives since mass production began in 1943. Before antibiotics, minor wounds frequently caused fatal infections, childbirth was life-threatening, and bacterial diseases like pneumonia, tuberculosis, and syphilis were common causes of death. Penicillin is arguably the single greatest life-saving invention in history.