The masses of Undead found their way to the land of the living through a planar rift, opened when the Trumps of Doom were sounded. Now that they are among the living, they seek solely to destroy all living creatures and add them to their soulless ranks. The most common type of Undead appear as skeletal remains of their once living bodies. However, other types of Undead exist as well, including Wraiths and the dreaded Reaper.
Undead have little "society" of which to speak. They often conquer and occupy the towns and cities of other races. Some Undead are needed to do basic work to maintain the housing and buildings in these cities, but most Undead exist only to destroy everything else around them and expand the numbers and reach of their people.
Already dead, Undead have little to fear. They can be destroyed most often by brute force, but most are immune to the effects of poison and fear and are highly resistant to lightning, fire and cold. Slow moving and expendable, Undead often resort to victory by numbers. Expecting such tactics, many a town has been surprised and overrun by more powerful Wraiths or by swift-moving Demons, Hellhounds, and Werewolves.