When I first put up these webpages I figured anyone who stumbled upon them probably already knew of Nurgle. Apparently I was wrong, Nurgle now has a PR department and a videographer.
The one line definition of Nurgle is: Nurgle is one of the four Chaos Powers according to the background for Games Workshop's various games. I also wanted to avoid the standard definitions you get on the dozens of half assed Warhammer/Warhammer 40,000 web pages out there. So I give you two excerpts from Lieber Chaotica Volume 3:
Fear is the first step on the road to His hell, and hopelessness is the chain by which He binds his slaves. Sorrow is his nourishment. Horror gives Him form. He preys on those who would submit to bitterness and those who closet themselves in misery, while life moves on around them.
He is terror in the face of decay and disease, and He is inaction in the face of all that is perceived as inevitable.
He is our impotence to resist the ravages of time, and He is our morbidity. He is revulsion and self-deceit, and He is the acceptance of defeat. He breathes His cynicism into our souls and binds us to His will.
He is Grandfather Nurgle, and He is obstinate, self-indulgent, despair.
And another quotation from the same source, note the contradiction inherent in Nurgle, too many Johnny come lately Nurgle followers miss this important aspect.
It appears that Nurgle's entire purpose is to promote endless suffering and misery throughout all the Mortal Realms. Yet, conversely to this, I have heard tell that Nurgle is supposedly deeply caring towards His mortal and daemonic servants, and is full of unexpected humour...
Games Workshop did not invent Nurgle. Games Workshop did not invent much actually. Their fantasy universe borrows heavily from Tolkein obviously. Their sci-fi universe borrows heavily from such diverse sources as Frank Herbert's Dune, the Aliens Universe, and Walt Disney's "101 Dalmations". One popular source of inspiration is mythology. The name Nurgle (Nergal) comes from Summarian/Babylonian mythology. In fact spotting the inspiration for various Games Workshop ideas is a game unto itself. At least GW does not claim originality a lot of the time.