Because Kalki has not visited us yet, we can not say much about him. Like the other nine incarnations of Lord Vishnu, he is expected to incarnate when our ethical condition becomes deplorable — too low to be improved by saints. Scriptures say that in the last phase of kaliyuga, which may be a few hundred thousand years away, people stop engaging in good karma altogether, hypocrisy defeats God’s remembrance, citizens renounce their prudence, and spiritual knowledge is completely lost. This sets the platform for God’s final visit to Earth to trigger another cycle of four yugas, beginning with satayuga.
Kalki’s name is mentioned in many Puranas, including the Vishnu Purana, the Srimad Bhagavata Purana, and the Harivamsha Purana. According to the Vishnu Purana, he will be born to a Brahmin named Vishnuyasa in a village named Shambhala to annihilate all the wicked rulers and citizens of Earth. After Kalki guides the remaining humans towards their appropriate dharma over the last few days of kaliyuga, their minds will get purified as if they have “woken up at the end of the night.”
How can the author of the Puranas say anything about a future incarnation of Vishnu? Firstly, parts of the future can be seen by maharishis like Ved Vyas, who have divine vision. Secondly, though Kalki has not visited Earth in the current era, he has been here before in a previous cycle of yugas, according to Hinduism’s popular notion about incarnations. In fact, as Hindus believe, all incarnations of Vishnu are born repetitively in different eras or in different universes.