Kālidāsa
The most popular theory is that Kalidasa flourished during the reign of Chandragupta II, and therefore lived around 4th-5th century CE. Several Western scholars have supported this theory, since the days of William Jones and A. B. Keith. Many Indian scholars, such as Vasudev Vishnu Mirashi and Ram Gupta, also place Kalidasa in this period. According to this theory, his career might have extended to the reign of Kumaragupta I (r. 414 – 455 CE), and possibly, to that of Skandagupta (r. 455 – 467 CE).
Koka and Vikoka
The prophesy of Kalki and his battle with Kali appears in the Kalki Purana, a collection of predictions concerning when, where and why Kalki will manifest himself and what he will do. According to Hindu cosmology the world will experience four immensely long ages, or yuga, of which the Kali Yuga is the last. The Kali Yuga began in 3102 BCE and has 4270 centuries to left; Kali, the demon-king of the Kali Yuga, will be assisted by his generals, the twin brothers Koka and Vikoka, who will threaten to defeat Kalki by raising themselves from the dead faster than he can kill them. The god Brahma eventually appears to Kalki and reveals to him that no earthly or celestial weapon can kill the brothers if they are allowed to hold on to one another; the only way Kalki can defeat them is to separate and attack them both simultaneously. 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.