In Dungeons & Dragons, a lich is a wizard or cleric who seeks to defy death by magical means. They transform theirselves into an undead state by means of unholy magic and necromancy, storing their souls in magical receptacles called phylacteries. Occasionally, this metamorphosis occurs by accident as a result of life-prolonging magic.

A lich retains the abilities he or she possessed in life, but they also have had a virtual eternity to practice new skills and inevitably become very formidable. The most powerful example of a Lich in D&D is known as Vecna.

Many other works of fantasy fiction have borrowed the term and concept from D&D. Such works include the video games Eternal Darkness: Sanity's Requiem and the Ultima series, the Mage: The Ascension and Shadowrun role-playing games, and the novel Perdido Street Station by China Mieville. The warcraft III computer game by Blizzard Entertainment has also adopted the lich into their fantasy world. Liches, and various more powerful monsters based on them, are one of the worst threats in NetHack as well.