Alexander Fleming (1881–1955) was the Scottish bacteriologist who discovered penicillin in 1928, when a Penicillium mold drifted onto a staphylococcus culture and killed the bacteria around it — the chance observation that launched the antibiotic revolution and earned him the 1945 Nobel Prize.
Working at St Mary's Hospital in London, he noticed what others might have thrown away: a clear ring where bacteria could not grow. He isolated the mold's active substance, named it penicillin, and published — then watched the world ignore it for a decade.
