Kalki
Lord Vishnu has many avatars and in each yuga, he has revealed all of them except-the last avatar(tenth)-Kalki. It is said that in the last yuga Lord Vishnu will reveal this avatar too and the Kalki avatar will lead to the end of the world. The main reason is to destroy the wicked, to restart the new creation, and to restore the purity of conduct in people's life. This avatar will be seated in a white horse with a drawn sword blazing like a comet. Earlier that White horse came from the Third eye of the lord Shiva in the form of fire that has been converted into the White Horse by Lord Brahma.
Read more about this topic: Yuga