Nurgle is the Great Lord of Decay and the Master of Plague and Pestilence, his carcase is riddled with disease and infestation. Nurgle is also the Lord of All because all things, no matter how solid and permanent they seem, are liable to physical corruption. Indeed, the very processes of construction and creation foreshadow destruction and decay. The palace of today is tomorrows' ruin, the maiden of the morning is the crone of the night, and the hope of a moment is but the foundation stone of everlasting regret.
Once we comprehend what it is that the Chaos Power Nurgle embodies, it becomes easier to understand what might otherwise seem a contradictory or even perverse nature. On the one hand he is the Lord of Decay, whose body is wracked with disease. On the other, he is full of unexpected energy and a desire to organise and enlighten.
The living know that they will die, and many know that they will live with disease or other torment, yet they drive this knowledge into a corner of their minds and keep it there with all manner of dreams and activity. Nurgle is the embodiment of that knowledge and of the unconscious response to it, of the hidden fear of disease and decay, and of the power of life which that fear generates.
Nurgle is the eternal enemy of the Chaos Power Tzeentch, the Lord of Change. Nurgle and Tzeentch draw their energy from opposing beliefs. While the energy of Tzeentch comes from hope and changing fortune, that of Nurgle comes from defiance born of despair and hopelessness. The two Great Powers never lose an opportunity to pit their forces against each other, from mighty battles on the Chaos Wastes, to complex political intrigues among mortal men.
The Great Unclean Ones are the Greater Daemons of Nurgle. In the case of other Chaos Powers, Greater Daemons are servants, in albeit immensely able and powerful ones. This is not quite true of Nugle's Greater Daemons, who are each more or less a facsimile of Nurgle himself, both physically, and in terms of their personality. In other words, it may be said that every Great Unclean One is also Nurgle.
A Great Unclean One is sometimes referred to as Nurgle or Father Nurgle by his underlings, although of course he has his own daemonic name.
A Great Unclean One certainly looks lke Nurgle - a gigantic figure bloated with decay, disease, and all imaginable kinds of physical corruption. The skin of the daemon is greenish, necrose and leathery, its surface is covered with pockmarks, sores, and other signs of infestation. The inner organs, rank with decay, spill through the ruptured skin and hang like drapes about the girth. From these organs burst tiny creatures called Nurglings which chew and suck upon the nauseous juices within. Such foulness represents the truth of the universe, of decay and the end of all things.
Yet in character the Greater Daemon is neither deathlike nor morbid. In fact the opposite is true, Great Unclean Ones are motivated by all the trivial human enthusiasms which drive the living. They are ebullient and vociferous, full of a natural enthusiasm to organise and achieve. They are driven by a gregarious and even sentimental nature and hold their followers dear, even referring to them as their children and taking a noticeable pride in their appearance and endearing behaviour.
This combination of physical corruption and energetic endeavour is the most extraordinary characteristic of Nurgle's aemons. It can be seen mostly clearly when the Great Unclean One and his daemonic followers appear in the material world.
The horde travels in a great cavalcade of covered wagons, bringing with it all the pestilences and ills that befall the living. The wagons are in no better physical condition than the daemons within. Their shrouds are tattered and rotten, their frames splintered and bent, and their metal-work pitted and rusted. Yet within the plodding caravan of Nurgle all is bustle and activity as the Great Unclean One prepares to launch a festival of decay and destruction upon a human village, a thriving town, or any opposing army. For Nurgle's visitation is like that of a travelling circus or great fair, except that the entertainment it offers is disease, sickness, and death.