Cataclysm

(a.k.a. Palios Pseftis)

Pay no attention to the scheming elf of indeterminate age and origin behind the curtain. That's just Palios. He's nice.
This is, of course, a blatant lie, but what else should you expect from the Fundamental Avatar of disorder, chaos, and destruction. Cataclysm is the personification of Pandemonium and is compelled to tear down all that has been built up.
And he revels in his work.
He delights in double-crossing, scheming, beguiling, and causing as much mayhem for men and gods alike; even more so if he can coax his victims into their own undoing. Far better to talk a king into waging a bloody war across the land as opposed to just killing all those peasants himself.
Unfortunately for Cataclysm, he was just a bit too good at his cosmically assigned task, and the stewards of the mortal lands, The Former , decided the world would be better off without him. After a long and arduous campaign, they captured Cataclysm's essence and sealed him away in the heart of their domain in the Liminean Wilds of Horizon, and there he sat for a long, long time.
During his imprisonment, he had all the time in the world to think. At first, he gleefully considered all the fun ways he would make the Former's lives a living hell, but as the millennia wore on, his thoughts turned to something far darker: introspection.
Cataclysm is a being of absolute anarchy. He cannot help but to destroy. It's his nature, his calling, his purpose, some might say. A purpose. A doctrine to be followed. Rules. The god of anarchy was playing his part like a good little pawn, just like every other miserable creature under the stars. This, of course, did not sit well with Cataclysm.
He spent many an age contemplating this revelation and how to subvert it, but everything he came upon fell short. He could not simply circumvent his nature; he could not become an Avatar of peace, love, or little donuts. He could not abstain from destruction. It was, after all, a compulsion. He could not even take the "easy" way out like a mortal could, for he could not die. He was a pawn on a chess board and all he could do was continue to march forward like all the rest.
Or.
He could break the board and flip the table it sat upon.
And so he set about to do exactly that. For the remainder of his tenure sealed away (first by the Former and then again by Shepherd after a brief respite), he plotted and schemed on how to break the world and the very system that confined him. He would assume a mortal guise and stir up as much chaos as he could in order to strengthen his own power as well as destabilize the very foundations of the world. When the time was right, he would pull it all down: he would take the threads that tethered the many Planes of Existence and smash them together until there was nothing left but an endless expanse of roiling plasma. And the best part? The world would be so busy tripping over itself to try and stop him that no one would be able to do anything about it until it was too late...

Other Names

As a being that predates even the earliest civilizations, the entity currently referred to as Cataclysm has gone by countless names. Some that have survived into modern times are Tahrovin (dragon), Vicium (giant), Nihil (primordials), Tul'mith (elves), Asmodeus (scholars), Jekenheil (old humans), and Ra Mush'sha (demons).

The Masquerade of Palios Pseftis

Cataclysm's chosen façade to deal with the lands of mortals was a shadar-kai elf called Palios Pseftis. Ostensibly, Palios was the scion of a family of shadar-kai that escaped the Shadowfell and settled in a rustic village deep in the northern reaches of Lapis Teras. When he came of age, he set out on a grand journey to unravel the mysteries of the world; heading north into Kentro, then east into Requiem, and finally north again into Horizon.
In actuality, "Palios" has only walked the world for a little over a decade. Cataclysm remained imprisoned in the idol even after the goliath warlord Lazaros "Warbringer" Inulethai found it hidden away in the island ruins jutting out of the Agate Sea. Lazaros carried Cataclysm around with him for years until finally the idol was broken during The Day of Long Shadows in Crucible. Once free, Cataclysm took on the guise of Palios and wasted no time ingratiating himself into multiple prominent and influential organizations.
He arrived in the city of Sigil and quickly wormed his way into the role of arcane advisor to King Aurum Fortis III, where he worked closely with the king's Crown Mages. In Kentro, he was inducted to the board of M.A.G.I. and gained access to an entire province worth's collection of knowledge and expertise. Finally, he ingratiated himself with the mages of The Lunar Forum , and when the Forum's previous Archmage died suddenly, maneuvered to undercut his replacement and put himself in the role of Archmage.
Palios used his stations and access to knowledge to map out and find the vast network of Foci that dotted Archaios. He then traveled to them and pumped them full of magic; overcharging them and causing them to boil with wild magic. For the Foci that were imbued within organic material, like the Elder Yew of Luma Forest, this resulted in an apparent "corruption," where the foci-imbued object would grow rapidly and violently, like it was sprouting cancerous tumors.
Slowly but surely, this raised the amount of ambient magic in the world, agitating the Planes and their "orbits" around one another. It also infused monsters and magical creatures with a new energy, bringing them out from the far flung corners of the world and back into the view of mortals; many of whom considered these creatures to be little more than legends.
All the while, Palios did all he could to sow animosity and violence across the land. He woke the Antecean sorceress Rapture from her state of stasis in the hopes of reigniting her feud with the lich Shepherd in Horizon. He stoked the fanaticism of the Heralds of Aevilok, who infiltrated swathes of society in Kentro and Requiem on his behalf. He whispered of a coming existential threat to King Aurum of Sigil and watched in glee as he plotted to annex the cities of Penance and Cognance into a new empire in the name of stability. Finally, he pointed the Reckoning, the warlord Lazaros' alliance with the hierarchy of giants, towards awakening the Tarrasque: an apocalyptic beast of legend in and of itself.
And with all eyes squarely on Horizon and Requiem, Palios was free to conduct his own work in Kentro in all but complete anonymity. He constructed a network that tethered the Mithral Spire in Eodur with the Planar Spires of the other Planes of Existence with the intent of smashing them all together in a Convergence that would atomize everything; reducing the planes to one singularity of fire and nothingness. True to his plan, he was able to trigger the device before anyone was the wiser. 

A Plan Thwarted

However, the tenacity of mortal proved too much even for something as seemingly-inevitable as a Collision of the Planes, and Cataclysm was ultimately once again sealed away where he could do no harm to the world at large. Even in defeat though, Cataclysm left his captors with an ominous warning: he has gotten used to imprisonment, and no matter how they may scheme to contain him, eventually they will wither, fade away, and once again he will be free. They have not saved the world, merely delayed its destruction. 
As of 1590, it is believed that Cataclysm is still contained, with the esoteric Wardens of Cataclysm remaining in the shadows; valiantly watching for even the slightest rattling of his chains.

Divine Classification

Fundamental Avatar

Alignment

Chaotic Evil

Church/Cult

The Heralds of Aevilok

Age

Unknowable

Current Residence

Elemental Chaos