Alexander Fleming

Returning from holiday in September 1928, Fleming found a mould growing on a culture plate he had left out, and a clear ring around it where the bacteria had died. He published, and then largely moved on: turning the mould into a medicine took Florey and Chain another decade.

He shared the Nobel Prize with them in 1945 and used his lecture to warn that misusing the drug would breed resistant bacteria — which is exactly what happened. He is buried in the crypt of St Paul's.