Kui is a one-legged beast from the Classic of Regions Beyond the Seas:
"Seven leagues from the coast, in the middle of the Eastern Sea, lies Liu Bo Mountain. On the mountain there lives a beast which resembles a bull with cyan skin, no horns, and one leg. When it enters or appears from the sea, it is always accompanied by violent storms. It's skin glows like the sun and the moon, and the sound it makes is like thunder. When the Yellow Emperor (黄帝 huáng dì) attained one, he used its skin to make a drum, and he would beat the drum with the bones of the "thunder beast." The awe-inspiring sound could be heard from over 500 leagues away."
In the battle between the Yellow Emperor and Chi You (蚩尤 chī yóu) it is said that the Yellow Emperor beat his Kui-Skin Drum (夔鼓 kuí gǔ) to boost the morale of this troops whilst simultaneously making his enemies tremble with fear. It was a vital part of his victory.