Penicillin (1928)

Penicillin has saved an estimated 200 million lives since mass production began in 1943, reducing bacterial pneumonia mortality from 30% to under 5%—a 25-percentage-point drop. Fleming's discovery in 1928, developed by Florey and Chain into a therapeutic by 1940, made childbirth safer and treated once-fatal infections like syphilis. It ranks above the printing press in direct lives saved, proving the greatest life-saving invention in history.