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THE PANTHEON OF EXANDRIA
When the Divergence transpired, the Divine Gate was established. A powerful barrier between the Material Plane and the divine realms, the Divine Gate both sealed away the Betrayer Gods and the Prime Deities to their respective domains in hopes of salvaging the new age and preventing another Calamity.
Should the Divine Gate be destroyed by the unanimous effort of the Prime Deities, all powers will be unleashed and Armageddon will be imminent. Thus, the gods patiently watch their creations from beyond the veil, lending what small power and chosen minions they can send through the gate to aid their faithful in their goals and pursuits.
The Founding
Long ago, this world was one of tumultuous and chaotic forces. Naught but unbridled fires, and churning, saw-like rock made up its substance. Through the ashen skies of Creation Primordial, the gods came from beyond the ether, new and formless. The gods brought forth creatures to inhabit Exandria, before splitting into two factions in the war against the Primordial Titans: the Prime Deities and the Betrayer Gods. The Prime Deities, with the help of their mortal champions, ultimately destroyed the Primordials and banished the Betrayer Gods from the Material Plane.
The Age of Arcanum
Over time, some of the peoples grew arrogant. Seeing their arcane gifts as proof the gods held no sway over their fate, some began to believe that, with enough understanding, they could become as powerful as the gods themselves. They broke open the Betrayer's prison, where they had been spawning hungry creations of their own, and released them back into the Material Plane.
The Calamity
No record remains of the terrible war that followed, but its effects are still felt today. The sheer magnitude of the energies unleashed in the ensuing battles of gods and mortals alike was enough to fray the boundaries holding back the elemental chaos, spilling unbridled destruction into the world. It completely rearranged the known flow of magical ley energy across Exandria.
The Divergence
Hoping to seal away the Betrayer Gods for good, the Prime Deities retreated from the Material Plane. Behind themselves and their defeated brethren, they erected a barrier known as the Divine Gate, which would prevent any god from physically crossing over into mortal realms.
PRIME DEITIES
The circle of Prime Deities includes the leaders and luminary creators that battled the Primordials and instigated the Founding, forging the mortal races of Exandria. They represent a spectrum of light, protection, love, death, and all other facets of freedom and life in the world. While some gods may disagree and squabble, they exist in a subtle alliance to maintain the sanctity of life and their respective creations.
BETRAYER GODS
The Betrayer Gods are the deities who strayed from the ideals of the Founding and embraced the destructive chaos of the Primordials or grew selfish of their own creations. The Betrayer Gods rarely work together, since they see each other as threats to their own plots and goals. This very weakness allowed the Prime Deities to defeat and banish them, ending the Calamity.
LESSER IDOLS
After the banishment of the pantheon in the Divergence, the mortal realm was left to its own devices. Beyond the trickle of divine assistance allowed by the Divine Gate, mortal creatures are now the keepers of the future of Exandria. This vacuum of influence has given rise to a number of powerful entities who may not rival the gods in their abilities or influence, but now unchallenged, can amass a modest following of their own. These idols present themselves in many different ways, some as honorable guardians of the helpless, and others as the tyrannical gods they aspire to be. Many of these beings have ambitions they wish to fulfill and can offer great power to mortals in exchange for their servitude.
With All Credits to Matthew Mercer
You have made such a wonderful world for us to explore and I hope this helps a few DM's introduce their players to it.
More Credits
Thanks also to the wonderful folksover at criticalrole.fandom.com where a bunch of this stuff came from.