Happy St. George's Day - UK

April 23 marks the saint’s day of England’s patron saint St George.  Saint George and the Dragon by Gustave Moreau.Who was Saint George? Why is he England's patron saint?
In hagiography, as one of the Fourteen Holy Helpers and one of the most prominent military saints, he is immortalised in the myth of Saint George and the Dragon. 
English schoolchildren are always taught that he was a knight who slew dragons but is there more to the historical figure?

According to legend, St Georg...