The Tsol'teth are the descendants of the Tsol'aa warriors, known as Qui'anar, who fought during the battle at Nishnatoba. Upon returning home, these Tsol'aa began to disagree with others of their race in regards to how to treat other races, (considering these races inferior, and worthy only of enslavement.) While it is possible the effects of battle may have hardened the Qui'anar, other factors may have been at work, though no solid evidence has been found for any current theories as to what may have caused this change.
The Tsol'teth left their cousins in an exodus that eventually led them far below the earth, to the Underrealm. There, they enslaved other races - goblins, hobgoblins, ogres, and an insect-like race that may have been horkvali - to serve them and worship them as gods. Their language splintered from Tsol'aa and became the dark language of the deeps that it is now. During the travels of Nicator, in his search for Seleucar, the Tsol'teth took an interest in the surface world once more. Three Tsol'teth in particular were involved in the war to come: Agith'maal, Terrin'ukia, and Gattan'lier, the strongest amongst them being Agith'maal. These Tsol'teth summoned forth the demon prince Pazuzu in hopes of learning how they might better achieve their new goal, the destruction of all mortals who roamed the surface world, though the demon lord's simple answer, "Seleucar," frustrated them.
First Black Wave
The Tsol'teth were eventually able to divine the meaning of this word, but were unable to travel to the surface world with their army of slaves, as the sunlight burned them. They prepared for some time, and sent curses and plagues to weaken Nicator and his followers, while amassing a great army and training them to better understand the surface world. Eventually the Tsol'teth slew their goblinoid and horkval slaves in a great ritual. From their corpses, the Tsol'teth took "spiral ribbons of future creation" and used these objects to give life to fiercer, more heartless slaves with an insatiable bloodlust and an immunity to the sun. Only their hobgoblin captain, Blademaster Matic Ridley, was spared, trained in the ways of the surface world and used by his masters to help prepare the new army for battle. Matic Ridley became vengeful, however, feeling the true soul of his people had been lost.
In what was to be known as the War of the Deeps, each of the three Tsol'teth took their forces to different major city-states of the realms: Agith'maal to Seleucar, Terrin'ukia to Shallam, and Gattan'lier to Ashtan. They nearly decimated these cities until Agith'maal was betrayed by Matic Ridley, who pulled away the cloak of darkness protecting the Tsol'teth lord and stabbed him in the back. Matic Ridley aided the Seleucarians, and they were able to defeat Agith'maal and his forces by tearing out the Tsol'teth's heart. An unfortunate side effect of this was that the occultist Adchachel devoured the heart to gain essence, and later went mad.
Seleucar was able to aid Ashtan and Shallam after the defeat of Agith'maal, defeating the other Tsol'teth, though not without many casualties.
During an unknown period in history, the Tsol'teth ally known as Lachesis, the Spider Queen led a force against the goblins and hobgoblins of Khazadmakan in Azdun for reasons unknown. Lachesis' main camp lay on the eastern edge of the upper level, while Khazadmakan was situated at the northwestern edge of the lower level, north of the graveyard in which Zsarachnor resides. Khazadmakan fell to Lachesis' forces, and the slain goblinoids either became victims of the fell magic of the Tsol'teth, or the thirst of Zsarachnor's undead, for they themselves became shambling zombies and ghouls in the end. It may be that the surviving goblins struck up a peace agreement with Lachesis, for today they dwell above Azdun in the Dakhota Hills, but are allowed to enter the dungeon for the purpose of mining.
Adchachel went mad, but only four years after having consumed the terrible heart of Agith'maal. During this span, he sired children, many of which ascended to nobility. Among these descendants was Castomira Brangwin, the Duchess of Aster Malik, whose Tsol'teth legacy, which sought nothing but the fall of the aboveground world, drove her into the depths of a madness that steeped Seleucar in the oft-romanticised Wars of Succession.
No more was heard of the Tsol'teth until the Modern Age, when an unknown Tsol'teth invaded the previously hidden Barony of Dun Valley, slaying its inhabitants with the aid of ogre and orc slaves. Before his plans could be realised, however, he was betrayed by one of his slaves, Vukub Ysin'zhu. An apprentice of the Tsol'teth, Zh'risia, survived, and managed to manipulate the orc, Kroul. Kroul was under the command of Vukub, and through him Zh'risia nearly succeeded in his vile plans, the extent of which are unknown. Eventually, an army of Achaeans, grouped from many walks of life and united in their purpose to stop the machinations of Vukub, invaded the fortress and found Zh'risia there, ruining his plans and slaying him after a great battle.
Second Black Wave
The first stirrings of what would become the Second Black Wave are likely to have begun with the mysterious series of deaths and murders that culminated in the death of Thoth, God of Death, at the hands of Slith, and then afterwards to The Underworld Rebellion. So was hinted by Agith'tai, one of the Tsol'teth invaders, shortly before perishing at the hands of Tenith'oru-now Parni d'Sangre. Though the exact relationship, if any, between the now-Lord of the Underworld and the Tsol'teth is not well understood, it was revealed that the purpose of the latter in slaying Thoth was to harvest His essence so they could create a God of their own as an anchoring point for their race. Thus did the world witness the birth of Tlalaiad, the Genesis.
As a last ditch gamble, the adventurers of the five city-states of Sapience rallied the help of Parni de Sangre and Yuddhisthira to erect a barrier against the rising Black tide. Raising magical stanchions and reinforcing them with barrier shards each year, the subterranean horde is held at bay only through the vigilance of Achaeans everywhere.