The corpulent and foul Great Unclean One known as Ku'gath began, humbly enough, as a diminutive Nurgling serving Nurgle. He once sat upon the great shoulders of the Lord of Decay as no more than a mite whilst his master concocted the most virulent toxin ever created. Tumbling from his nesting place whilst Nurgle was mixing the noxious contents, Ku'gath fell into the rusty cauldron. Taking a great draught of the filthy contents, the minor daemon quickly swelled with power. Invigorated by the potent cauldron of poxes, Ku'gath continued to drink and drink until the cauldron was empty. The miniscule form of Ku'gath grew into a mighty Great Unclean One. Laughing with joviality at the antics of his new creation, Nurgle was pleased with Ku'gath and what he had become; the embodiment of the perfect disease. Realising that his creator was not perturbed by this turn of events, Ku'gath soon realised that he had robbed the Plaguelord of his greatest achievement. Since that day, Ku'gath has sought to recreate the toxic miracle that birthed him.
Standing apart from his fellow Greater Daemons, Ku'gath is a sombre creature. He does not revel in the gurgling delights of infection and plague. For the Plaguefather is contemplative and industrious, forever traveling throughout the Realm of Chaos and the mortal universe, seeking every ingredient and sickness imaginable in order to re-create the perfect disease once more. Ku'gath moves across reality atop a palanquin carried by a mound of thousands of straining Nurglings, searching for the right combination of poxes and blights to replicate Nurgle's dark miracle. The palanquin is also loaded the alchemical paraphernalia of Ku'gath's mobile laboratory, so that he can continue to experiment and distill the procured poisons of millions of worlds and the furthest reaches of the ever-changing realms of the Warp.
To field test his creations, Ku'gath unleashes his virulent plagues during times of war in order to test the effectiveness of his various concoctions, wiping out whole armies. In battle, Ku'gath hurls his pestilent Nurglings at his enemies, for the tiny daemons grow within the daemon lord, each carrying a unique blend of the virulent elements that created the unique Great Unclean One. With detached interest Ku'gath watches each particular infection and their symptoms take hold of the victims of his field experiments. Capturing those corrupted by his diseases, he takes them back to his lair within the manse of Nurgle himself to observe them more closely. Thousands of cages, containing creatures of every known species from all across time and space, stretch into the darkness of this vast, ruinous lair. The victims of Ku'gath wail, gibber and moan in the gloom, desperate for the death that will be long and agonising in the coming.
- Battle Missions, pg. 17
- Codex: Daemons (4th Edition), pg. 49