Koka and Vikoka
According to the Kalki Purana, the twin brothers Koka and Vikoka serve as generals under the demon Kali, overlord of Kali Yuga. In their battle against Kalki, the 10th and final avatar of lord Vishnu, the brothers display their mastery over the dark arts by raising themselves from the dead faster than Kalki can kill them.
The Kalki Purana states they are the grandsons of Shakuni and sons of Bakasura. These are not the same as the similarly named Shakuni and Bakasura from the Mahabarata. The former are father and son, whereas the latter are unrelated.
Lord Brahma eventually appears to Kalki during the battle and reveals to him that the twin devils had received from him a boon of "immortality". No earthly or celestial weapon can kill them if they are allowed to hold on to one another. The only way for the dark duo to die is to separate and attack them both simultaneously. Sri Kalki then forces himself between the two and lands crushing blows to each demon’s temple at the same time. They both die, this time for ever.
- René Guénon, the reign of quantity and the signs of the times, chapter 25, the fissures in the great wall.