"The Forgotten are more powerful than any creature any mortal human has faced. They are swift, strong and they cannot be slain. Their forms are rebuilt in sepulchers in their homeland. Their blades are passed down through their generations, each new iteration inheriting the armor and weapons of the one before. There are females and males, but they do not mate save for the Empress and the Emperor. Their children are the Dark Knights, the most vicious and maleficent of the Forgotten. You fought a foot soldier, bred only to kill. It had probably died a thousand times before, it had no fear of you but it had no allies. Outnumbered, a Forgotten will flee to a place where it may find advantage. Forogtten have no voices but for the whistles of the dust within their withered bodies. They are animated from the evil sands the Forgotten themselves live within, the City of Mordre'kai is their home within the shifting sands of their home realm.
I've read of the Traveler, when he walked the Far Veil before he stepped beyond the Gates of the Scorpion and into the realm of the Great Darks, Ahn'quoria. The Forgotten were once like us, mortal humans snatched from Aurica during the Dark War against Set. They were corrupted by dark magic and thrown to the shifting sands of Ssinda. What emerged was the Forgotten, bred with the strength of ten men and the dark power to slice through any enchantment, turn back any spell, and the Dark Knights are well known for their dark magic powers. They corrupt the very earth they walk on, their blades are chilled with dark ice rime from the cold tombs they are created in. Everywhere they step, things freeze and wither. The Forgotten soldiers, archers and mages that act as foot soldiers are paltry sand zombies compared to the vast intellect of a Dark Knight. Some say they are blessed by the Great Dark Lord of Endless Winter who rules from the dark tower of Arctis Tor somewhere within the lands of the Great Darks..."
Silas spoke to Kin, his long explanation rambling on and on. Outside, things had been swallowed by the darkness of the tunnel built by the Guardians. The image floating in the metal bits was that of a Dark Knight, evil spiked armor glowing with malevolence. "Dark Knights may die, but their spirit cannot be slain in this world. It must be faced in the Far Veil to release one from the possession and corruption of the spirit of a Dark Knight, long ago one man on earth was corrupted by this evil force. Though I have not the heart to speak his true name, he was once an angel and paragon of goodness before falling to far as to be cast even from hell's fire to the Far Veil's cold touch. He Whom Rules The Nameless is merged with a Dark Knight of immense and terrible power, and I pray none shall ever face him in battle."
Silas dismissed the metal shavings and gathered them up. "Tell me Kin, have you ever heard of the Archivum?"