St. George became patron saint of England in 1415 AD, over a thousand years after his death. His cross forms the national flag of England, and is featured within the Union Flag of the United Kingdom, and other national flags containing the Union Flag, such as those of Australia and New Zealand. Actually, St. George never set foot in England.
St George was born to Christian parents in 270 AD in Cappadocia, which is now Eastern Turkey. He moved to Palestine and became a Roman soldier, but later resigned and protested against his pagan leader, Emperor Diocletian, who led the persecution of Christians in Rome. His rebellion led him to be imprisoned and tortured, but he did not abandon his faith. He was eventually dragged through the streets and was beheaded on 23 April 303 AD. His death is now commemorated on that day every year.
The story about St George slaying a dragon reportedly took place in Libya. The story claims that a dragon lived near a town’s only fresh water spring and had been attacking the local population. Townspeople had sacrificed several maidens from the town to appease the dragon, but without success. The next sacrifice was due to be the princess Cleolinda. Instead, George fought the dragon, slayed the beast and saved the princess. To show their gratitude, the people of Selene converted to Christianity.
Modern-day scholars believe the dragon in the story represented the devil or evil at the time.
You can read more in Wikipedia at http://en.wikipedia.org/wiki/St_George.