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In the Dungeons & Dragons fantasy role-playing game, demon lords (also known as Abyssal lords in 2E AD&D) are demons who have gained great power and established a position of preeminence among demonkind.

Each demon lord has a unique appearance and set of abilities. Most control at least one layer of the Abyss. A demon lord, when slain in a plane other than the Abyss, is banished to the Abyss for 100 years, whereas "ordinary" demons, including the mightiest balors and mariliths, risk being reborn into a lesser form (or not at all). The most powerful demon lords are demon princes. "Demon lord" and "demon prince" are self-proclaimed titles; unlike the archdevils, the chaotic evil demon lords do not have a rigid hierarchy. However, first edition AD&D did claim a demon can only be called a prince if he or she rules an entire plane of the Abyss, thus Orcus implied by his title to rule at least one plane of existence, while lesser lords did not.

Demon lords wage eternal war with each other, often seeking ways to expand their holdings into other layers and at the same time defend their personal domains from rival lords and scheming underlings. Demogorgon has for many years been the most powerful demon lord, and he proclaims himself Prince of Demons. Orcus and Graz'zt contest his title, as does the obyrith Obox-ob, who once held that title.

Most demon lords have secretive mortal cults who seek to elevate their lords to godhood through prayer and sacrifice. Book of Vile Darkness details a number of prestige classes for mortal disciples of demon lords, as does the "Demonomicon of Iggwilv" feature currently running in Dragon magazine.

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