(Sanskrit कल्कि) According to the prophesies of India, in his tenth and final incarnation Lord Vishnu will incarnate himself as the Avatar Kalki, who will come riding his white horse and with his blazing sword in his hands. At the end of Kali Yuga (the present eon) He will punish all evil doers in this world, destroy this world, and recreate a golden age again. As it says in the ancient Vishnu Purana:
When the practices taught by the Vedas and the institutes of law shall nearly have ceased, and the close of the Kali age shall be nigh, a portion of that Divine Being who exists of his own spiritual nature in the character of Brahma, and who is the beginning and the end and who comprehends all things shall descend upon the earth. He will be born as Kalki in the family of an eminent brahmin, of Sambhala village, endowed with the eight superhuman faculties. By his irresistible might, He will destroy all the barbarians and thieves, and all whose minds are devoted to iniquity. He will then 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 pellucid as crystal. The men who are thus changed by virtue of that peculiar time shall be as the seeds of human beings and shall give birth to a race who shall follow the laws of the Krita Age, the Age of Purity. Vishnu Purana 4.24
This is the Buddha Maitreya of the Mahayana Buddhists, Sosiosh of the Zoroastrians, and "The Faithful and True" of the book of The Revelations of St. John 19:
And I saw heaven opened, and behold a white horse; and he that sat upon him was called Faithful and True, and in righteousness he doth judge and make war. His eyes were as a flame of fire, and on his head were many crowns; and he had a name written, that no man knew, but he himself. And he was clothed with a vesture dipped in blood: and his name is called The Word of God. And the armies which were in heaven followed him upon white horses, clothed in fine linen, white and clean (without ego). And out of his mouth goeth a sharp sword (the Word, the knowledge), that with it he should smite the nations: and he shall rule them with a rod of iron (Iron is the metal of Mars, of Samael): and he treadeth the winepress of the fierceness and wrath of Almighty God. And he hath on his vesture and on his thigh (next to the phallus) a name written, KING OF KINGS, AND LORD OF LORDS.).(See also Maitreya).