Nagulib

The Nagulib are the most powerful vassals of the imprisoned Formless. As Karakush confesses to Minalan in Preceptor:

They are called the Nagulib... the most powerful of the vassals of the Formless. And like the Formless, they were imprisoned by the Vundel as well, though by different means. It was they who arranged the great calamity, many eons ago, that formed the jevolars. They are brilliant sorcerers, and have managed to contact us over the millennia in order to use us for their own ends.Karakush, Preceptor

They are, functionally, demons — Karakush himself eventually calls them that:

What better name for such a malevolent folk? They might as well be. It was from them that Korbal first secured the secrets to our deathlessness. They cannot die, as we understand the term. Not even the Deeps were strong enough to hold them, so they were consigned by the last Celestial Mother to the only prison that would hold them. If they are slain, they will return thence, and re-form themselves into even more powerful bodies.Karakush, Preceptor

Their history with Callidore is catastrophic. The Nagulib engineered the Dragonfall — the ancient impact that "brought a mountain from the sky and nearly ruin[ed] the Vundel," and which formed the jevolars in its aftermath. They contacted Korbal before his entombment, bargaining secrets of deathlessness for rituals, messages, errands. After his return they resumed the relationship. The spiders Mycin Amana deployed at Darkfaller were a gift of the Nagulib; so were the dragons drawn through the molopor. Their payment, Karakush fears, is coming due — and even he, who would see humanity chained and humiliated, would rather lose the war than pay it.

The Nagulib are thus classified among the cosmic powers of Callidore, not its native peoples: imprisoned, deathless, patient, and contacted only through the molopor at the heart of the world.