In the medieval age, the saints were popular heroes. They were soldiers who fought in the Christians' battles. Also, they were friends of the God and their stories were appreciated by other people, so people were more interested on the lifes of the Saints in the wars than the conquests of the kings. The reason was that to follow a Saint's story was a special way to arrive at God. That's why, Saint George was recognized a Saint Soldier.
He was a roman soldier under Dioclesiano emperor. His anger in the battles made to win the position of Dioclesiano's advisor. Nevertheless, this emperor killed the Christians and George refused to do it. Finally, he went to the prison and Saint Santiago appeared. He said to George that he would be prisoner during seven years and just like a miracle, he would die three times, he would be revived but at the fourth time, he would die for ever. That happened and finally, the emperor gave him the freedom if he made a sacrifice. Saint George prayed and the God burned all the people included the Dioclesiano's wife. At the end of the story, the emperor ordered to cut the head of the Saint George and he never stood up because it was the fourth death.
In XIII Century, the dragons represented confusion, dark and disaster. The dragon is related with the snake of the Edén garden, messenger of the original sin.