The story of the being known as Hajar is two fold.
In one existence it was the spirit of a long dead protector who couldn't stop the originator of the Plague or Madness that ravaged the The City so long ago. The cult of Lamashtu was too powerful and once the undead came in swarms, his eternal rest did not come. His regret held him tethered. He begged Ra for retribution.
In another, a Osirin native, in the recent timeline failed to stave off some of the Undead upon his party, and succumbs to the failure. The last thing seen, the shambling of a mummy.
Osiris, seeing their fall and noting the still burning embers of hope the two souls had, used his might and rebrithed the old into the new...
Thus Hajar nar jundi Chosen of the Sands was born, Not fully one or the other, but blessed with a second chance in one form. To discover that which has passed and that which may happen. To prevent such a fate from befalling humanity once more. Given mastery of the sands and the rising sun to aid in this endeavor.