Wights and Wraiths
Wights are the spirits of great warriors and fighters who would not rest. The urge to battle is strong in them and they will fight any perceived challenger. If left to their own devices wights will either stay and guard their burial site or someplace with meaning to them, or they will wander the land looking for a fight. If summoned or commanded by a necromancer they become lethal soldiers of death. They are not the shambling, groaning legions that are the lesser dead. Wights move with purpose and are as lethal as the warriors they were in life... if not more so since it is not until their bodies are thoroughly destroyed that their souls will leave the realm of the living and they are defeated.
Wraiths are the spirits of (typically evil) sorcerers and magic users who sought to cling to life. Often they were driven mad by their magics when they died. Some have hold of their minds but have refused to rest in peace. Unless commanded by a necromancer wraiths typically stay put. Either in the place where they died or protecting some arcane knowledge or item they do not wish to relinquish even in death. Most dangerously, wraiths still command the magic they did in life and though not so great at hand-to-hand combat they are formidable spell casters with a seemingly inexhaustible supply of mana.
Alignment (if any): evil - undead
Life expectancy: n/a