What is Alexander Fleming famous for?

Alexander Fleming is famous for his discovery of penicillin. For this discovery he won the Nobel Prize in 1945, approximately 10 years before his death. Fleming's breakthrough came in 1928, which was the first of many breakthroughs in the field of antibiotics.

Before penicillin was invented, people were largely defenseless against bacterial infections and diseases. Penicillin, now known as one of a number of antibiotics, was the first way to combat infections and diseases. The discovery by Fleming is estimated to have saved hundreds of millions of lives. While bacteria have evolved over time, many can still be treated successfully with penicillin.