Demonlord

Demon lords, also known as Abyssal lords, are fiends who gained great power and established a position of preeminence among demonkind. Over millennia, these demons had amassed tremendous power and authority over their domain.
Demon lords approach close enough to divinity that they cannot cross portals to toher plane on their own, though sufficient mortal magic can summon them.

“As creatures of chaos incarnate, demons have no unified culture. The only modicum of order that exists for a demon is the one imposed upon it by a more powerful demon—and the moment that a demon rises high enough to assert its authority on others is the very moment that rivals begin to subvert that authority.”
— The Demonomicon

Hierarchy

Each demon lord has a unique appearance and set of abilities and rule over at least one layer of the Abyss. Those that control several layers and rise higher in power give themselves the title of demon prince. Both "demon lord" and "demon prince" are self-proclaimed titles by those who have gained enough power and influence. The demonic fiends are in an eternal struggle, edging and fighting for dominion over one another. Unlike the archdevils, the chaotic evil demon lords do not have a rigid hierarchy.
A demon lord, when slain in a plane other than the Abyss, is banished to the Abyss for a thousand years, whereas ordinary demons.

History

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.
Most demon lords had secretive mortal cults who sought to elevate their lords to godhood or to please the demon lords such as the Cult of Ashlesh.