Who is Kalki? (Kalki avatar)

In Hinduism, Kalki (Devanagari: कल्कि; lit. destroyer of filth) is the tenth and final avatar of the god Vishnu in the current Mahayuga, foretold to appear at the end of Kali Yuga, the current epoch. The Purana scriptures foretell that Kalki will be atop a white horse with a drawn blazing sword.
Chronologically Krishna is described as the eighth Avatar of Lord Vishnu. This happens in Dvapara Yuga. According to Kalki Purana, Kali demon will rule the earth and bring sin and misery to the people. When the first stage of the Kali Yuga begins, the varna system will deteriorate. Soon after this, the second, third, and fourth stages of the Kali Yuga begin. During the second and third portions, men will forget the name of God and no longer offer Yagna to the Devas. During the fourth portion, Canibalism will be virtually universal among the humans. To solve this problem the pious Devas will gather before Brahma for a solution. Near the end of this yuga, the Devas will then journey to Vaikunta to seek help from Lord Vishnu. Lord Vishnu will then descend to Earth to end the Kali Yuga.