Alexander Fleming was a Scottish bacteriologist who accidentally discovered penicillin in 1928—the world's first widely used antibiotic. He noticed that mold growing on a petri dish killed the surrounding bacteria, ushering in the antibiotic era and fundamentally transforming human medicine.
Fleming came from a humble background and entered medicine through self-determination. During World War I, he witnessed many soldiers dying from infections and devoted himself to finding a germicide. Penicillin saved countless Allied soldiers' lives during World War II. In 1945, Fleming shared the Nobel Prize in Physiology or Medicine with Howard Florey and Ernst Boris Chain, and his discovery is hailed as one of the greatest medical breakthroughs of the 20th century.
