Kalki - Devanagari: कल्कि; is the tenth and final Avatar of Vishnu who will bring to an end the present age of darkness and destruction known as Kali Yuga. He will establish a new era based on truth, righteousness, humanism and goodness, called Satya Yuga.
The Agni Purana explains that when the evil men who pose as kings begin to feed on human beings and try to destroy the righteous, Kalki, as the son of Vishnuyasha, and Yajnavalkya as his priest and teacher, will destroy these evil men with His weapons. He will establish moral law in the form of the fourfold varnas, or the suitable organization of society in four classes. After that people will return to the path of righteousness. (16.7-9)
The Vishnu Purana also explains that, "When the practices taught in the Vedas and institutes of law have nearly ceased, and the close of the Kali age shall be nigh, a portion of that divine being who exists of His own spiritual nature, and who is the beginning and end, and who comprehends all things, shall descend upon earth. He will be born in the family of Vishnuyasha, an eminent brahmana of Shambhala village, as Kalki, endowed with eight superhuman faculties. By His irresistible might he will destroy all the mlecchas (Barbarians) and thieves, and all whose minds are devoted to iniquity. He will reestablish righteousness upon earth, and the minds of those who live at the end of the Kali age shall be awakened, and shall be as clear as crystal. '" (Book Four, Chapter 24)
The Kalki Purana explains when man stops offering yagna to the gods, Vishnu himself will descend to earth to rid the world of evil. He will be reborn as Kalki to noted Brahmin family in the city of Shambhala. As a young man, He will be mentored in the arts of war by Parashurama, the sixth incarnation of Vishnu. He will then set out across the world battling evil kings and false prophets. He finally defeats Kali and brings about the Satya yuga. Having completed His mission, He will assume his four-armed form and return to heaven as Vishnu.