Around the 4th Century in Libya, a town was being terrorised by a dragon and the villagers would feed it sheep to appease it but gradually they ran out of sheep so the King devised a lottery system to feed it local children.
One day his own daughter was chosen and as she was being led out to the lake a Turkish knight named George happened to ride past and offered to slay the dragon if the people converted to Christianity. They all did, the dragon was slayed and the English decided to call him a Saint and dedicated the 23rd April to celebrating him.
Critics may point out that saving the girl in exchange for a mass conversion wasn't very generous and a better man would have saved the girl and killed the dragon for nothing but let's not be picky.
As well as England, St George is also the patron saint of Portugal, Venice, Beirut, Malta, Ethiopia, Georgia, the Palestinian territories, Cyprus, Serbia and Lithuania but besides that we still claim him as our own and each year some berk appears on TV wearing a suit of armour and bang on Patriotically about what England means, which it turns out is very little.
Unlike the Irish with St Patrick, the Welsh with St David or even the Scots with St Andrew, St Georges Day passes with hardly a flicker of recognition or interest from one of the countries that he is the patron Saint of and we seem perfectly fine with that and we would probably have had him up for cruelty to animals if he tried that killing dragons bit these days.