Kui is a one-legged beast from the Classic of Regions Beyond the Seas:
东海中有流波山，入海七千里。其上有兽，状如牛，苍身而无角，一足，出入水则必风雨，其光如日月，其声如雷，其名曰夔。黄帝得之，以其皮为鼓，橛以雷兽之骨，声闻五百里，以威天下
"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.