Kai, also known to all as "Kai the Collector", is the main antagonist of DreamWorks' thirty-second full-length animated feature film Kung Fu Panda 3.
He is a supernatural bull who appears as Po's third enemy and the former brother-in-arms of Master Oogway and later becomes a powerful evil Spirit Warrior. Thus, he can steal chi from Kung Fu warriors and turn them into Jade Zombies. His scheme is to defeat every Kung Fu master.
Many years ago, Kai and Oogway fought together as brothers-in-arms, and were close friends. One day, during an ambush, Oogway was gravely wounded, and Kai carried him for days, searching for help, until they came upon a secret panda village, where the pandas used the power of their chi to heal Oogway instantly. Oogway was fascinated by the power and the pandas taught him how to utilize it. However, Kai became extremely jealous, selfish and possessive, and wanted the power all for himself. He decided to take chi from others rather than give it. Seeing the damage Kai's obsession would cause, Oogway confronted his fallen friend in a fierce battle that shook the earth until finally, Oogway triumphed, banishing Kai's body and soul to the Spirit realm, forever. However, Oogway feared Kai would somehow return to the mortal world and finish his evil plan and the only one could stop him would have to be a true master of chi.
And he is reprised by J.K. Simmons in the English dub and Koji Ishii in the Japanese dub.