Alexander Fleming seems like less of a genius and more of a lucky guy. We've most of us heard the story about how he discovered that mold could be a good thing: his original name for penicillin was 'mould juice'. Antibiotics were born.
So screw him. I'm giving this one to Maurice Hilleman.
The reasons are many. First, as the 21st century starts out, the dependency on antibiotics is becoming apparent as a mixed blessing. Vaccination, on the other hand...well, who doesn't get vaccinated any more?
Not that Hilleman invented the vaccine. (Thanks, Pasteur!) Nor did he convince the public of it's usefulness and safety: that honor goes to Jonas Salk, whose polio vaccine saved generations.
Hilleman's many reasons are that he invented the vaccines for: measles, mumps, Hep A and B, pneumonia, meningitis and chicken pox. That's seven out of thirty.
In the U.S. 1 out of every 5,000 people had polio in the 40s and 50s. How many people used to get chicken pox, or measles? Pneumonia? Don't think these are minor diseases, either. In developing nations the top five causes of infant death are: respiratory, dehydration, malnutrition, malaria, and measles. Hilleman's work continues.