Demon lord

Demon lords, also known as Abyssal lords, were archfiends 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.

"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 of Iggwilv

Hierarchy
Each demon lord had a unique appearance and set of abilities and ruled over at least one layer of the Abyss. Those that controlled several layers and rose higher in power gave themselves the title of demon prince. Both "demon lord" and "demon prince" were self-proclaimed titles by those who had gained enough power and influence. The demonic fiends were in an eternal struggle, edging and fighting for dominion over one another. Unlike the archdevils, the chaotic evil demon lords did not have a rigid hierarchy, though they appeared in greater numbers throughout the Blood War.

A demon lord, when slain in a plane other than the Abyss, was banished to the Abyss for a hundred years, whereas ordinary demons, including the mariliths and glabrezus, risked being reborn into a lesser form, or not at all.

History
Demon lords waged 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. Obox-ob was the first demon lord to hold the title of "Prince of Demons", a coveted status symbol, followed by Miska the Wolf-Spider, and then Demogorgon. Orcus and Graz'zt contested this title, while Obox-ob desired to regain it.

Most demon lords had secretive mortal cults who sought to elevate their lords to godhood through prayer and sacrifice.

Obyrith Lords
Although obyriths were the oldest of the demonic races, and their lords among the most powerful, only a handful of obyrith lords survived the rebellion of the tanar'ri demons. Known obyrith demon lords included:
 * Dagon: Prince of the Darkened Depths, Dagon was a primeval leviathan of a demon lord whose presence brought a fear of the sea and all that lurked beneath the water. He was a maddeningly massive being, ancient and powerful even by obyrith standards, and yet also an isolationist that acted as an oracle for the tanar'ri from within the depths of the Shadowsea.
 * Dwiergus: Referred to as the Chrysalis Prince, Dwiergus was a house-sized soup of everchanging limbs that ruled The Fleshforges, an undulating, protoplasmic realm of hate and hunger. The eldritch, primordial demon lord was driven primarily by the desire to reshape all living things into demonic lifeforms, and implanted the overwhelming urge to remove a body part out of the irrational belief the Prince had tainted it.
 * Obox-ob: The original Prince of Demons, Obox-ob was said to be the first obyrith to rise from the primordial matter of the Abyss, an entropic demon lord of putrescence that could inject others with raw chaos stuff that consumed their bodies and souls. After being deposed and forced to retreat to the deep Abyssal realm of Zionyn, he was reduced to a patron of poison and spreader of entomophobia as the Prince of Vermin.
 * Pale Night: The so-called Mother of Demons that came to be known by the name Pale Night was an unknowable being of such awful shape that reality itself tried to hide her. To see the truth beyond the veil was to court death, her incorporeal form a harbinger of insanity and dreadful births. Seen as a mother figure by many in the Abyss, there was no knowing what horrors she was truly responsible for spawning.
 * Pazuzu: Prince of the Lower Aerial Kingdoms, Pazuzu declared all Abyssal skies as his, and few cared enough to fight him over such a claim. Though once an obyrith lord, he had somehow "evolved" into a kind of intermediate form between obyrith and tanar'ri, gaining a bond to evil creatures of the air in place of his once-maddening form. Upon the calling of his name thrice, he appeared to offer corruption disguised as aid.
 * The Queen of Chaos: Her actual name stricken from history, the self-styled Queen of Chaos led the obyriths to war against the rest of reality, specifically against the forces of law. Certainly a force of change, the Queen was behind the fall of Obox-Ob, and had killed, imprisoned, and weakened those obyriths that opposed her. She retreated to The Steaming Fen after her defeat and despite the hopes of a few obyriths, hadn't been seen since.
 * Ugudenk: Referred to as the Squirming King, Ugudenk was a worm-like obyrith that primarily dug through his Writhing Realm. Seemingly immortal, it was speculated he was himself an Abyssal layer, his maw a feeding tendril that sometimes reached across the multiverse to devour at apparent random. His presence brought a fear of that which burrowed, and the crippling thought he could burst from the ground at any time.

Demon Princes
The most powerful of the demon lords, aside from the obyrith lords, were called demon princes. These were tanar'ri demons. Known tanar'ri demon princes were:
 * Demogorgon: The third Prince of Demons, he was a monstrous demon with a humanoid, scaly body, two mandrill-like heads, tentacles in place of arms, clawed feet, and a tail.
 * Orcus: The self-proclaimed Lord of the Undead, Orcus had the legs and head of a ram, a long tail, bat-like wings, and a humanoid body. He was the archenemy of Demogorgon and Graz'zt.
 * Graz'zt: Also known as the Dark Prince, Graz'zt was a guileful, cunning demon lord that appeared as a handsome, muscular humanoid with obsidian skin, six small horns on his head, pointed ears, and six fingers on each hand. He was the archenemy of Orcus and Demogorgon.
 * Baphomet: The Prince of Beasts looked similar to a gigantic minotaur with coarse black fur that covered his body. He was widely worshiped among minotaurs as well.
 * Yeenoghu: Similar in appearance to the gnolls who worshiped him, Yeenoghu, who was also called the Lord of Savagery, maintained a feud with Baphomet.
 * Juiblex: Juiblex, the Faceless Lord, was a monstrous, multi-colored ooze covered in red eyes. He was mainly concerned with causing destruction.
 * Fraz-Urb'luu: The self-styled Prince of Deception was a mysterious, winged demon lord.
 * Kostchtchie: Kostchtchie was a demon lord who corrupted frost giants into worshiping him, and called himself the Prince of Wrath.
 * Malcanthet: The Queen of the Succubi and one of the more subtle demon princes.
 * Zuggtmoy: A demon princess whose powers and concerns primarily involved fungi.

Other Demon Lords
The vast majority of demon lords were tanar'ri, but only a few were demon princes. The rest were simply called demon lords.

Former Demon Lords

 * Arlgolcheir
 * Astaroth
 * Zanassu

Appearances

 * Novels
 * Archmage