Archdevil

The archdevils were powerful, unique devils. The most powerful archdevils were the Lords of the Nine.

Hierarchy
The position of archdevils in the hierarchy of Baator was clear: archdevils were the most powerful and were, therefore, on top. The most powerful of the archdevils were the archdukes, also called the Lords of the Nine. Other archdevils were dukes, ruling portions of a layer, generals, or bureaucrats of various sorts.

Archdevils of Avernus

 * Zariel: The Lord of the First and commander of the diabolical armies in the Blood War, Zariel was a fallen angel who had been appointed to her archdukedom by Asmodeus himself.
 * Bel: A general under the command of Zariel and a former archduke himself.
 * Under Tiamat's rule of Avernus, her generals included the archdevils Amduscias and Malphas.

Archdevils of Dis

 * Dispater: The Lord of the Second, Dispater rarely left his Iron Tower due to his extreme paranoia.
 * Lilis: The loyal consort of Dispater.
 * Titivilus: Although not very powerful personally, Titivilus was Dispater's closest adviser.
 * Bitru: A duke of Dis in the service of Dispater.
 * Arioch: A vassal of Dispater who meted out vengeance on those who dared defy his master.
 * Biffant: The loyal provost of Dispater.
 * Merodach: A duke of Dis.
 * Alocer: A duke of Dis.

Archdevils of Minauros

 * Mammon: The ruler of Minauros and patron of greed.
 * Glwa: Mammon's consort after Glasya left him.
 * Bael: A powerful general in the service of Mammon.
 * Focalor: The cautious seneschal of Mammon.
 * Caarcrinolaas: A duke of Minauros.
 * Melchon: A duke of Minauros.

Archdevils of Phlegethos

 * Fierna: The official Lord of the Fourth.
 * Belial: The father of Fierna as well as her predecessor, Belial was in part the power behind the throne of Phlegethos.
 * Chamo: An archdevil who served Belial as Legate of Abriymoch; his loyalties during Fierna's rule were unknown.
 * Balan: A duke of Phelgethos who served Belial; he remained loyal to Belial even after the archduke "retired".
 * Bathym: A duke of Phlegethos who served Belial; he chose to cast his lot in with Fierna after she rose to power.
 * Gaziel: A duke of Phlegethos who served Belial; he remained loyal to Belial even after the archduke "retired".

Archdevils of Stygia

 * Levistus: The Lord of the Fifth was imprisoned in an iceberg by Asmodeus for past crimes. He was therefore forced to telepathically relay instructions to his minions, even as he also had to deal with his predecessor's continued existence.
 * Geryon: The deposed Lord of the Fifth, Geryon was a savage archdevil who sought to reclaim his former position.
 * Agares: A vassal and duke under Geryon's reign; he found a new position as a commander under Levistus's rule.
 * Machalas: The weakest duke who served Geryon; he found a new position as a commander under Levistus's rule.

Archdevils of Malbolge

 * Glasya: The daughter of Asmodeus, Glasya was the Lord of the Sixth.
 * Tartach: Formerly the legate of Moloch, he abandoned Baalzebul to serve Glasya.

Archdevils of Maladomini

 * Baalzebul: Also called the Lord of Lies, the Lord of the Seventh was the repulsive fallen angel who was once called Triel.
 * Baftis: The quiet First Consort of Baalzebul.
 * Lilith: formerly the consort of Moloch, she later became after Baalzebul's Second Consort.
 * Neabaz: Called the Herald of Lies, he served as the herald of Baalzebul.
 * Barbatos: The Marshal of Maladomini.
 * Abigor: A duke and general of Maladomini.
 * Zepar: A duke and general of Maladomini.
 * Bileth: Formerly the tribune of Moloch, he became a general in the service of Baalzebul after returning to Maladomini.

Archdevils of Cania

 * Mephistopheles: The Lord of Cania was always plotting against Asmodeus.
 * Baalphegor: Consort of Mephistopheles and quite possibly the reason why the Lord of the Eighth was not demoted.
 * Hutijin: A duke of Cania and powerful general who loyally served Mephistopheles.
 * Bele: The justiciar of Cania.
 * Adonides: The steward of Cania.
 * Barbas: An archdevil who served Mephistopheles as chamberlain.
 * Bifrons: A powerful duke and vassal of Mephistopheles.

Archdevils of Nessus

 * Asmodeus: The Lord of the Ninth and King of the Hells, Asmodeus was a deity in his own right.
 * Adramalech: The Chancellor of Hell and Keeper of Records, Adramalech answered only to Asmodeus.
 * Phongor: The dreaded Inquisitor of Hell.
 * Buer: A duke of Nessus.
 * Bune: A duke of Nessus.
 * Morax: A duke of Nessus.
 * Rimmon: A duke of Nessus.
 * Zagum: A duke in the service of Asmodeus.

Other Archdevils
Of course, due to the nature of politics in the Nine Hells, archdevils wound up exiled or dead at various times. Some exiles remained in the Nine Hells (such as Geryon and his court, listed above), while others were forced to leave completely.

Additionally, the dragon goddess Tiamat spent some time as an archdevil after her Untheric aspect was killed. She was ruler of Avernus during some of her time there. Another archduke that wasn't an archdevil was Malagard the Hag Countess, who ruled Malbolge before Glasya. She was actually a supremely powerful night hag, rather than a devil.

Exiled Archdevils
Some archdevils, former archdukes, were exiled or imprisoned, but survived. These included:
 * Gargauth: A once-powerful archdevil who left the Hells for unknown reason.
 * Malkizid: Also called the Branded King, Malkizid was a fallen solar who became an archdevil. He was exiled after earning Asmodeus' disfavor, and went to reside in the Blood Rift.
 * Nergal: An archdevil exiled by Asmodeus.
 * Moloch: Former Lord of the Sixth, Moloch was exiled for rebellion by Asmodeus.
 * Herodias: An archdevil who once served Geryon as a magistrate; he was driven into exile after Geryon lost power.
 * Amon: A vassal and former duke who was formerly in the service of Geryon; he was driven into exile after Geryon lost power.
 * Malachlabra: The outcast daughter of Dispater.

Other exiled archdevils included Armaros, Azazel, Bist, Cahor, Caim, Duskur, Jaqon, Kochbiel, Malarea, Nisroch, and Rumjal, all of whom lived as wandering outcasts in Avernus.

Deceased Archdevils

 * Bensozia: The consort of Asmodeus and Queen of the Hells, Bensozia was slain by Levistus.
 * Naome: The consort of Belial and mother of Fierna.
 * Beherit: The original Lord of Sixth.
 * Cozbi: The consort of Geryon; she was destroyed after he lost power.
 * Gorson: The bailiff of Geryon; he was destroyed after Geryon lost power.