Gygaxian demons in the Gord books
I have read some of those awful Gord books that Gygax wrote. I mainly skip most of them and concentrate on his treatment on the Lower Planes, which fascinates me. There is a hostof new demon princes (with familiar ones under different names).
In the books, the following demon lords are listed as: Fraz-Urb'luu/Var-Az-Hloo, Juiblex/Szhublox, Lolth/Arachne, Verin/Vuron. Other undetailed MM2 demons had slightly different spellings like Eblis/Eblitis, Socothbenoth/Socothbenothas, Azazel/Azazael.
Demon princes that were mentioned, and some had crop up in other websites, developed by others:
Mandrillagon, a sibling of Demogorgon, resemble a huge blue-faced mandrill, rules two layers.
Ushablator the Chaos Horror.
Zortolagon, said to be one of the most powerful demon princes.
Bulumuz, decribed in the web somewhere as a lord of madness.
Elazalag, an abat-dolor princess, of the same species as Graz'zt.
Cagrino (according to myths, related to the chargin grues/demons)
Marduk, the king of fire demons who is one of the "Monarch of Demonium"
Ogrijek, lord of the four winged hawk-man zubassu
Trobbo-gotath, a "greatest demon of earth".
Apepi , a cobra-headed lord who wields a kopesh.
Uliel - Probably a balor that serves Zuggtmoy.
Shabriri - one of the proto-demons, said to be multi eyed. He is NOT Cabiri as some suggested.
Palvlag - a protodemon of fire.
Nergel/Nergal - in the books he is a minor prince of the undead, specifically umbral undeads.
Levithan (probably Leviathan) - undescribed but in real world myth, an enormous female seas monster.
Lugush - undescribed, prehaps a corruption of "Lugh".
Ariax - a prince whom Graz'zt had triumphed over and whose holdings expanded Graz'zt empire to eight planes. Perhaps same as Areex.
Vastyi - the toadmaster, supposedly an amphibian demon lord, although some identified him as the god Wastri.
Other lordlings include Vloorm, Agadin, Zerkaar, Chidun, Zomar, Yuibiri, Arioch (named used for a devil), Nexroth (name used already for a pit fiend).
Speaking of Verin/Vuron, his "stats" were listed in For Duty and Deity, and basically, he is a male marilith, which I think go against what we know and accept about him.