Kalki (Sanskrit: कल्कि), also called Kalkin is the prophesied tenth and final incarnation of the god Vishnu. He is described to appear in order to end the Kali Yuga, one of the four periods in the endless cycle of existence (Krita) in Vaishnava cosmology. The end of the Kali Yuga states this will usher in the new epoch of Satya Yuga in the cycle of existence, until the Maha pralaya (dissolution of the universe).

Kalki is described in the Puranas as the avatar who rejuvenates existence by ending the darkest and destructive period to remove adharma (unrighteousness) and ushering in the Satya Yuga, while riding a white horse with a fiery sword. The description and details of Kalki are different among various Puranas. Kalki is also found in Buddhist texts, for example the Kalachakra-Tantra of Tibetan Buddhism.

The prophecy of the Kalki Avatara is also told in Sikh texts.

The name Kalki is derived from Kal, which means “time” (Kali Yuga). The original term may have been Karki (white, from the horse) which morphed into Kalki. This proposal is supported by two versions of Mahabharata manuscripts (e.g. the G3.6 manuscript) that have been found, where the Sanskrit verses name the incarnation to be karki.