Saint George was martyred under Diocletian early in the fourth century; within a century, churches were being dedicated to him.
The legend of Saint George sprang up much later: a city in Libya had been feeding a rapacious dragon with lambs; when they ran out of lambs, they drew lots for human victims, the lot eventually falling upon the King’s youngest daughter, who was walking out to sacrifice when George happened by.
On the screen at Filby (1; c.1470), he is in company with Cecilia, Catherine and Peter, standing on the dragon, thrusting a lance down its throat. Not far away, at Ranworth (2; c.1470), he is on one of the parclose wings trampling a vividly blue dragon (twinned with that other dragon-slayer St Michael, on the opposite wing).
Sometimes St George appears in bigger compositions. In themural (c.1506) on the north wall at Fritton (3), he is shown mounted; note the princess and her lamb behind St George and the dragon. Best of all is Wellingham (4; c.1529), where George is again mounted, trampling on the dragon (spot the baby dragon right at the bottom!). The King, Queen and others watch from the city battlements, while the kneeling princess is again accompanied by a lamb.
For more, read Samantha Riches, St George: Hero, Martyr and Myth, Sutton, 2000.