St George was apparently a Palestinian christian who joined the Roman army then later on refused an order from the Emperor for soldiers to give up christianity and make sacrifices to pagan gods. The Emperor at the time had known George's father so cut George a bit of slack, offering bribes of money and land to convert.
George refused and was beheaded. Not a very good model for the English to hold up as a saint as not only was George a troublemaker who refused to follow orders but he must have been incredibly stupid too. The Dragon bit was just a Troubadour's story brought back by Crusaders returning to Britain in the middle ages.
How he was adopted as our patron saint is Dorset's fault according to Bede A church at Fordington in Dorset, built by Alfred the Great, was set up to venerate George and had a feast day in his name. Everyone like's a good party so the feast day started to spread around the country. On top of that the merchants in London thought that George's flag, the red cross on white background, looked cool (and didn't cost much to make) so started using it on their ships and for the Crusaders armies that they'd raised and funded. Eventually the flag just came to represent England.
Here endeth the history lesson... Our patron saint is just a dumb Palestinian troublemaker who was used as an excuse to get pissed in Dorset 
