The Ancients
"Seek not to hasten their return, any more than you would hasten an earthquake or tidal wave upon the land, for they are beyond the power to influence. To our hopelessly primitive understanding, they are unknowable. Yet if we are to stretch out infant limbs and learn to crawl to their presence we must be prepared to suffer the growing pains of madness on the way to enlightenment." High-Priest Sarento, The Codex Sagaticus
Beyond the limits of mortal understanding, far off in the distant reaches of space and yet somehow also lurking just beyond the thin veneer of reality separating this world from another, there reside The Ancients. Creatures of impossible age, understanding, and power, whose inhuman intellect so drastically outstrips mortal minds that one would go mad simply attempting to comprehend them.
However, this is not to say it has not been tried with some success. Like a force of nature itself, the brave, the foolish, the dedicated , and the mad have won secret knowledge of the nature of the cosmos from aligning their thinking to those of these most ancient ones.
Those who are Known
Ghaunadaur: The Slime Lord - The first god, it demands all life return to primordial ooze. Sacrifices to Ghaunadaur are disolved in acid.
Z̸͘҉á̴̢l̵̸̨g͘͝o̧̡͟:͜͡͠҉ ̵͟͝҉H̷̶̀e͘͟͏ ̢̕̕w̸̷h̶͢ǫ̸̛̀ ̸W̡͘͠ą̴̢̕i̷̴t͠҉̀ş̧̨͜ ̷̷͘B̸̸͘e̷͜͟ḩ̵̛͝ì͢͢͡n̴̶͟d̶̸͞ ͡͠͏T̶̛̛h̛̛é͘͝ ̷̵̛W̵͝͠a͝l̡͏̢҉l̸͝ ͘͜͏-͡҉̛҉̕ The eager one, he hungers for contact with the curious. Those who do his will, spread word of his coming far and wide.
Kos: The Lidless Eye that Sees - A tormented being that experiences time in reverse. Prayers to Kos for "eyes" are spoken backwards in the hopes of learning the future.
What they think of Other Pantheons
The Saints - "It is good to acknowledge the great works of those who came before you."
The Twins - "Perhaps they temper with light what they fear to look too deeply into in dark."
The Lords - "But a fraction of the madness that awaits us all."
The Scales - "As we are to dragons, so dragons are to the great Ancient ones, trifling lesser beings."
The Sun - "Even this mighty star will be swallowed upon their return."
The Watcher - "Let them turn their contemplation skyward and recoil in horror at what they learn of the true nature of reality."