St George was
a really hard guy to kill. According to Catholic tradition (although not according to official church doctrine) George was chopped into small pieces,
buried alive, and consumed by fire, only to be brought
back to life by God each time. When he was finally killed by
decapitation, milk flowed from his neck instead of blood.
He had some cool tricks, too, including raising the dead so they could be baptised, converting hundreds of people at a time, destroying armies and idols instantaneously through the power of his faith, and making dead beams of timber suddenly burst into leaf.
Despite an understandably incredulous stance on all this from the Holy Mother Church, he was canonized anyway by Pope Gelasius in 495, who included him among those saints "whose names are justly reverenced among men, but whose actions are only known to God".
The dragon story didn't come into play until the twelfth or thirteenth century, many hundreds of years after George's canonization, and the church does not recognize the killing of a dragon among his saintly deeds.
St George's Day is celebrated on 23 April.