[excerpt from Encyclopaedia Theologica: A Panoptic Primer on the Pantheon, Planes, and Patrons of Ylan, 5th ed., by the gnomish scholar Miriam Busslewickett]
The term “Old Gods” is commonly used to refer to the trio of entities Erebus, Uberlin, and Muriel. In truth, these names refer not so much to discernible entities as to the primordial forces of the multiverse; they are qualities we ascribe to represent the undefinable. Muriel, of course, represents creation; Uberlin, entropy; and Erebus, justice.
Religious scholars attest that these terms have been used in Ylan since before recorded time, by all races (although the specific rendering of the terms may vary slightly between languages). General theology holds that the Old Gods were responsible for creating the multiverse and all its planes, and that since creation they have resided (to the extent they can “reside” anywhere) on the plane of Oblivion. The names of the Old Gods are still invoked frequently to seek a general blessing — for example, one would be hard pressed to find a judge who does not cite the name of Erebus, or a warlord who does not call upon Uberlin, or a farmer who does not murmur the name of Muriel in his prayers. However, the Old Gods are understood to be remote from and unconcerned with the affairs of the Prime Material plane, inaccessible even through the Astral plane. For personal appeals, folk are much more likely to turn their prayers to their favored Patron.