Lilim

The Lilim were created by Lilith, Holy Mother of Darkness during the time of Emperor Shunaiman, using body modification techniques from the Age of the Giants as well as the powers of dark magic she had obtained from Shilen. Lilith took Human warriors and transformed them into something that could be called "undead" - they were not dead, being able to move around and fight, but they did not eat or breathe, nor did their bodies grow old or get sick. The Lilim actually could not die, as their names had been removed from the list of the dead. If one of them got killed in battle, he returned to the side of Shilen in the Underworld.

At that time the belief that one could attain immortality through martyrdom was prevalent in all religions, and since Lilith actually delivered on the promise, there was a never ending stream of volunteers who wanted to undergo the transformation into a Lilim soldier. The number of such zealots among Shilen's followers was so high that not to everyone of them could be given an opportunity to become a Lilim. This transformation process took some time, and priority was given to soldiers who had shown extraordinary achievement on the battlefield, to sorcerers who had attained great magical powers that could be used to bring about widespread destruction, and to assassins who personally delivered death to those whom the Goddess had marked out. From those among Shilen's devotees who fell not into these three categories, Lilith created a lesser tribe of undead, the so-called "Lith". While the Lilim formed the main fighting force in Lilith's campaigns against the Nephilim and Imperial Crusaders, the Lith were on guard duty in the Catacombs and Necropoli, also being responsible for upkeep and administration of the underground cities.

Source:

[1] The Secret History of the Elmoreden Empire