Alexander Fleming ( 1881 - 1955 )
Sir Alexander Fleming was born on  August 6, 1881 in Ayrshire, Scotland. The scottish biologist and inventor  is widely regarded for his discovery of penicillin, a drug that is used to kill harmful bacteria.He studied medicine from 1901 at the St. Mary's Hospital Medical
School in Paddington.

His work on immunology, bacteriology, and chemotherapy is considered  groundbreaking and highly influential.  
Fleming had a genius for technical ingenuity and original observation. His work on wound infection and lysozyme, an antibacterial enzyme found in tears and saliva,  guaranteed him a place in the history of bacteriology. But it was his discovery of  penicillin in 1928, which started the antibiotic revolution, that sealed his lasting reputation and which is actually considered as one of the most famous and fortunate accidents of the 20th century.
You better get ready for a funny and unbelievable story now:
Alexander Fleming didn't clean up his workstation before going on vacation one day in 1928. When he came back, Fleming discovered that one of his bacterial cultures had been contaminated by the spores of a certain fungus. When he wanted to throw the contaminated sample away he noticed that wherever the fungus spread, no bacteria settled there.
This phenomenon encouraged him to further experiments. He found out that the fungus produces a lethal substance for a number of species of bacteria. But particularly fascinated him the fact, that this substance did not attack the white blood  cells and was nontoxic to animals.
He named this metabolic product of the mold fungus “Penicillin” and published his findings in scientific journals.
Penicillin became the first and is still one of the most widely used antibiotics.
Alexander Fleming was knighted in 1944, because he took the medicine world one step further on the fight against lethal scourges like tuberculosis, syphilis, … .
Fleming was recognized for this achievement in 1945, when he received the Nobel Prize for Physiology or Medicine, along with Australian pathologist Howard Walter Florey and British biochemist Enst Boris Chain, both of whom isolated and purified penicillin.

Sir Alexander Fleming died on 11th March 1955. He is buried in St Paul's Cathedral.