It is of common knowledge that graveyards, burial mounds and ancient battlegrounds often are haunted by evil forces and should be avoided by night. These evil forces are spoken of as the Undead.
Undeads are brought to this plane of existance due to many a reason. Everything dead and decaying, animal corpses, farmers and fallen warriors can rise as minions in the cursed legions of Nitocris, the Ghoul Queen of the dead. A proper and respecful burial often prevents corpses to turn into disgusting beings such as hideous skeletons, rotting zombies, flesh-eating ghouls and wailing ghosts. Alas, no matter how frightening, these are just minor Undeads.
Supreme mages, kings of renown and legendary dragonslayers that die gruesome deaths are rarely seen again, at least not as minor undeads. They have been flirting with Death in many ways during their lifetime, thus Nitocris is aware of their coming and has already started to corrupt their souls. Chances are that they will turn into extremely powerful Undeads. If you stumble upon emperor liches, screaming wraiths, mummies and eyeless banshees, you better run for your life or face the might of Nitocris.
Undeads in general are very hard foes. This not only because of their horrific appearance, but also their spells. Sometimes even the strongest of warriors drops his sword as the Undead curses him, withering away his muscles. The once so agile thief, suddenly clumsier than a giant; the powerful magician, suddenly losing his memory and turning into a drooling fool. The list of curses is long, some even make you several years older.
The worst fact about the Undead is that they are often resistant or invulnerable to many natural ways of damage. Especially psionics and poison seem to have little effect on these creatures of the night. Fire, on the other hand, is known to be quite effective against many types of undead, burning their dry skin and garments.
The Sisters of Las and the Templars of Faerwon are sworn enemies of the Undeads and they are said to have been granted powers against the forces of darkness by their patrons. Most undeads recognize the aura of such good virtue and either fear or hate the bearer of light.