Vua Khú is the lord of the khú, the serpent- or dragon-spirits that inhabit the deep pools and rivers of the Mường country. In the tiered Mường cosmos he rules the watery world below, counterpart to Vua Trời above. The khú are feared as bringers of drowning and sickness who may seize a person's soul, and the Vua Khú stands at their head; propitiatory offerings and the intervention of the ritual specialist keep his subjects at bay. He belongs to the religious cosmology recorded in Mường ethnography rather than to a single narrative episode, and sources treat khú both as a class of water-monsters and, in the person of their king, as a distinct power of the underworld.