The Cold Keeper

The thing in the Karth Deep's unmapped dark — older than the wights, older than the Imperium, the reason the cold persists and the Meltwardens believe their work matters.

No one who has seen it fully has come back to describe it. The Meltwardens do not call it a creature; they call it the cold's memory. It has kept the Deep cold since before the Sundering. The Listening College's missing tuners, the Meltwardens insist, are not dead — they are simply being kept.