Sacred Haven of Debauchery

A lich (English: lich or lych, or German: leiche — “corpse”; [ˈlɪtʃ]) is, in modern fantasy, a mage-necromancer who has become undead, according to some versions — after death, according to others — instead of death. There is also a concept called the “ritual of eternal night,” during which a necromancer sacrifices a human (or several), seals his soul in a phylactery, after which he dies and is reborn as a full-fledged lich.

A lich is very difficult to destroy because, after its physical form is destroyed, it can be reborn with the help of a phylactery. An example of a phylactery is Koschei the Deathless’s chest, in which an object is sealed; destroying it is the only way to put him to rest. Koschei the Deathless himself is a prime mythological prototype of a lich.