The true origins of Zarach is unknown. His being is shrouded in secrecy and myth, even amongst the other gods. What is known is not when of how he ascended, but rather when he stepped to the fore and proclaimed his rule of the dead.
Zarach stepped into the realm of the divine to claim his power in the Times of Turmoil, some time before the God Wars broke out fully. It was a tense time in the mythical ages of Myrth and his ascension was met with friction in the realm of the divines.
Though none had heard of Zarach or his power before, he possessed the same divine, cosmic powers and presence as the other gods. None could explain the phenomenon. It was as if he himself had been resurrected from a place outside of time. He took on the mantle of death, all those who's souls were stuck in the limbo between realms, and those who's life force are halted in a singular cosmic state, as he himself is of un-death.