lich

In death, wizards of great power are sometimes able to turn themselves into liches. A lich is a skeletal, undead creature, whose magical powers can only be matched by its malevolence. The process of becoming a lich is very painful, but those who are powerful enough to become liches willingly undergo it: Liches are totally immune to any sort of mental attack, poisons, diseases and suchlike. They can also channel magical energy much easier than humans or any of the normal races, making them deadly adversaries. Liches are often seen leading great masses of lesser, undead warriors.