D&D: The Worth of Steel
"Outside the ordered universe is that amorphous blight… Sarlogll, whose name no lips dare speak aloud, and who gnaws hungrily in inconceivable, unlighted chambers beyond time and space…"
Sarlogll holds power over all things that seek to kill and collapse, who gains power from entropy and destruction. Without being kept in check by the delicate power balance among the Primevals, Sarlogll would consume the universe and all within it- and unlike Yshubotha, there would be no exceptions.
Sarlogll has no thoughts, no emotions, just a pure and unrelenting hunger for the end of all things. Consumption in this case can mean possession as easily as mastication, and Sarlogll is quite content to contaminate what it cannot devour.
Unfettered by morality or even basic sanity, the worshipers of Sarlogll use any tool necessary to achieve their dark ends. They are the bringers of pestilence and the weavers of madness, and cheerfully pay any cost in serving their ever-hungry master.