The Scar That Abides

Precious little is known about the force known as The Scar That Abides.
Their brand, a sigil of a burning helix around a jagged tear, has appeared across Adaxus' wrists, Forge's siberys shard, and the Unburned's implanted dragonshard. 
Fractions of prophecy scattered across years and miles have referenced them, mostly indirectly. 
They have been confirmed as the voice whispering to Adalror and Diiroehn through their aberrant dragonmarks, and may have gifted it to them.
A final confirmation has come from the Tangled Fane and the Forge of Hours. It was found that the Scar is a fiendish overlord, the immeasurably powerful demons created by Khyber at the dawn of time. Indestructible and native to the world, they were bound by the couatl who became the Silver Flame.
A piece of their prison was found bound to the land via the Tangled Fane, a shattered Khyber shard of gargantuan size which held part of their essence. This was believed to have been the source of the Du'rashka Tul, the Madness of Crowds, a curse wrought by the ancient dragons using the Scar's influence over revenge and discord to drive civilizations to destruction from within. 
Discoveries in Adaxus's personal journals confirmed they were the power that Adaxus made his pact with, a promise of servitude in exchange for knowledge and skill enough to remake giant civilization. These journals also contained the Scar's true name, ■■■■■■■■■■, and upon it being spoken aloud under particular circumstances it broke a condition that was keeping the Scar bound.
It was found that they are the incarnation of vengeance, patient anger, spite and discord. More than anything, the Scar is revenge, of old wounds that never healed, and of the terrible choice a person makes when they work for years, patient and methodical, to destroy those who have wronged them. They are served by fiends from both Khyber and Fernia, and the immolith demons seem to act as their particular servants.
It is known that Adaxus, and possibly The Dusksplinter Coven, serve them, and much of the discovered parts of the Draconic Prophecy refer to them and their imprisonment.

Divine Domains

Revenge, spite, patient anger, grudges

Divine Symbols & Sigils

A jagged tear, surrounded by a coil of flames

Divine Classification

Demonic Overlord

Age

~100,000 years

Circumstances of Birth

Created by Khyber as an intrinsic part of the world

"I am fear, and I am the youngest of many... while my siblings hold the old fears of mankind, the dread as the fire goes out and frostbite sets in, the terror and death of war, the roar of the predator that stalks the night... I am younger, born of societies, of cities...
I am the fear that love will turn to hate, of revenge and grudges, of pain never forgiven, the fear that every thing you have done is remembered and hated. When a misspoken word builds resentment in friends, when a friendly glance from a spouse to another feels like sharp betrayal, when every pain is held onto for years until revenge is wrought, I am there. In every wound that festers in the mind, every vendetta and feud, every injury savoured, every grudge satisfied, every escalation from suspicion to hatred to violence to war, I am there.
I am the Hate Everburning, The Festering Passion, The Patient King, The Prince of Vengeance, The Scar That Abides. I am ■■■■■■■■■■, and you all have served your purpose in this world. My champion will return to take the revenge he deserves, and this ruin will serve well as your tomb"