A dying (thankfully) species, the demon lord is a godlike entity that existed before the founding of the empire, its believed that the demon lords (or archedemons) as they were once called were some of the first beings to have powerful remnants, and in the current age the last two demon lords are some of the few currently-existing beings to hold remnants.
Even after the mass extermination of archdemons by heroes long past, the demons were driven underground into fire, scholars believe that something they found beneath the ground turned them into beasts of ash, they attempted one last desperate attempt to return to the surface, causing the humans of their time to massacre them one by bloody one. After this massacre, the demons turned from a once haughty and powerful race to a breed of dying animals. while the lesser demons still remain, mostly serving as vengeful murderers or mercenaries in less popular places, the demon lords were utterly annihlated. Once powerful beings became afraid of the unity of the weaker races, so they now to shy away from their foes. Their power has dwindled over time, but the last two demon lords are not to be underestimated- a cornered animal will still fight, especially if it clings on to some false, hopeless dream that it is not alone.
These last two demon lords are Naiyayaith the snake demon, and lord Tersis, the lady in crystal.
Naiyayaith, with Tersis's current status in question, is the last remaining demon who holds true to her nature. Naiyayaith is a master of cunning and deceit, she dabbles in the political nature behind the scenes every now and then, but fear of her final death keeps her from ever being seen. Rumors are abound that an extensive sahuagin assassin's guild has taken her in out of pity and respect for her treacherous nature.
Tersis is the second remaining demon lord, she is known as the lady in crystal. Unline Naiyayaith, Tersis's presence is known to be somewhere high within the greater floors of the crystal library, where she has made her own private realm where she studies in seclusion. Tales tell that she has covered her small realm in crystal in reverence for the same dragon the crystal golems revere. And the crystal golems respect her privacy so far as to guard her, making sure no potential demon-slayers trespass in her domain.