The Zhong Kui (鍾馗) story:
According to Song Dynasty sources, once the Emperor Xuanzong was gravely ill. He had a dream in which he saw two ghosts. The smaller of the ghosts stole a purse from imperial consort Yang Guifei and a flute belonging to the emperor. The larger ghost, wearing the hat of an official, captured the smaller ghost, tore out his eye and ate it. He then introduced himself as Zhong Kui. He said that he had sworn to rid the empire of evil. When the emperor awoke, he had recovered from his illness. So he commissioned the court painter Wu Daozi to produce an image of Zhong Kui to show to the officials.