Personification
Kali is the reigning lord of Kali Yuga and his nemesis is Sri Kalki, the tenth and final Avatar of Lord Vishnu. According to the Vishnu Purana, Kali is a negative manifestation working towards the cause of 'the end' or rather towards eventual rejuvenation of the universe. Kali also serves as an antagonistic force in the Kalki Purana. It is said that towards the end of this yuga, Kalki will return riding on a white horse to do battle with Kali and his dark forces. The world will suffer a fiery end that will destroy all evil, and a new age, Satya Yuga, will begin.
Read more about this topic: Kali Yuga