Many Hindu scriptures and tales passed down through generations describe Kalki as a warrior, much like Lord Ram, and it is believed that as the world undergoes four cycles, or Yugas, the Satyug, the Treta, the Dwapar, and the Kalyug, eventually a form will arrive to end the chaos that has started.
And as we live in Kalyug, an era marked with darkness, despair, and moral decay, the next avatar of Lord Vishnu will be Kalki. Kalki will appear to cleanse the world and reset the cosmic cycle, and a new Yuga will then start.