Literally birthed by Asharra in her home plane, the Aboleth (or Firstborn, as they call themselves) are her favored children. They are numerous in the Abyss, and range from 2 feet in length to massive specimens well over 20 feet long and over 6,000 pounds. The Aboleth serve their mother through their knowledge. Each Aboleth possesses not only it's own flawless memory and knowledge, but the memories of every ancestor it has ever had, and every being it has ever consumed. This means that over time the Aboleth gather an unfathomable amount of knowledge, all of which is transferred to their mother upon their death.

Asharra pays little attention to the doings of the Aboleth, giving them freedom unlike most of her children enjoy. As they cannot help but perform their task for her over the course of their long lives, she sees little need to dominate them. While every Aboleth is aware of the Dark Lady and her power, they do not truly worship her... though they all respect her power. Aboleth, like all of Asharra's children, have no souls, and are alien and unnatural beings upon the material plane.

Physically, Aboleth are fishlike amphibians that continue to grow as they age. They are a kind of hybrid of fish and eel with some insectoid and annelid qualities; they have long, tubular bodies, like that of an eel, but fish-like tails at the end and two fins near the head and a dorsal fin near the back. Their underbellies are orange-pink, and their topsides sea-green. A little bit back from the head are four long tentacles, two on each side, two on the topside and two on the underbelly. Their heads are roughly triangle shaped, with a spherical, somewhat beak-like nose. Above the nose are their three eyes, each one set atop the other. Tendrils and a few shorter tentacles dangle from the bottom of the head. Four blue-black slime-secreting orifices line the bottom of their bodies.

Aboleths have powerful psionic powers, being natural psions like their brothers the Illithids. However, the aboleth, like the other archetypal aberrations, has a much more fearsome ability: aboleths secrete a viscous grey fluid, much like mucus, which brings about a terrible transformation in air-breathing creatures. The skin of the victim is transformed into a membrane which allows it to breathe in water, but robs the creature of air-breathing. This allows the aboleth to keep slaves, which it dominates and keeps captive with its mind. This same mucus is the only way aboleths breathe at all – if robbed of the ability to extrude aboleth slime, they suffocate in water or on land. Out of the water, an aboleth's membranelike skin dries out quickly, but this does not prove fatal. Instead, the aboleth will eventually enter a state of suspended animation, called long dreaming, a fate considered far worse than simply dying. It forms a tough, waterproof membrane, but, once the membrane is pierced, liquid floods out and death is usually not far off for the aboleth. With the exception of the gained damage reduction and increased armor class, an aboleth out of water is simply a sitting duck.

Aboleths do not die of age, and so live on indefinitely barring violence or disease.

Terrible devastation has been visited upon the Aboleths with the complete destruction of the underdark. Those few close enough to the Abyss to flee have done so, though how long they might survive in that tortured plane is unknown.