Aboleths were fish-like amphibians of immense size, often reaching 20 feet (6.1 meters) in length and weighing up to 6,500 pounds (3000 kilograms), though they continued to grow as they aged and some fantastically ancient specimens might reach 40 feet (12.2 meters) in length. They resembled a bizarre eel, with long, tubular bodies, as well as a tail at one end and two fins near the head and another along the back. Aboleths' mouths were lamprey-like, filled with serrated, jawless teeth. Aboleth bodies were also segmented, like a worm or insect.
Aboleth underbellies were often orange-pink, while their topsides were typically sea-green. A little bit back from the head were four long tentacles, two sprouting from across each other on the top, and two more of the same on the underbelly. Their heads were roughly triangular-shaped, with a spherical, somewhat beak-like nose. Above the nose were their three eyes, each one set atop the other. Tendrils and a few shorter tentacles dangled from the bottom of the head. Four blue-black slime-secreting orifices lined the bottom of their bodies. Aboleth blood was green and thick, oozing like sap.
Aboleths breathed through a thick gray mucus-like substance, which covered their body and which they exuded from four pulsating organs along their body as they moved. If robbed of the ability to exude this slime, an aboleth would suffocate in water or on land alike. As such, an aboleth had to take care of its mucus. Out of the water, an aboleth's membrane-like skin dried out quickly, but this did not prove fatal in and of itself. Instead, the aboleth would eventually enter a state of suspended animation, called long dreaming, a fate considered far worse than simply dying amongst aboleths. During this process, the so-hampered aboleth formed a tough, waterproof membrane. However, if this membrane was pierced, liquid flooded out and death was usually not far off for the aboleth.
Aboleths did not die of old age and so lived on indefinitely, barring violence or disease.
Aboleths had powerful psionic powers and were natural psions like mind flayers and many other denizens of the Far Realm. However, aboleths had a much more fearsome ability, the capacity to secrete a viscous gray fluid, much like mucus, which brought about a terrible transformation in air-breathing creatures so unfortunate as to be caught in the stuff. The skin of the victim was transformed into a membrane that allowed it to breathe in water, and changed the creature's consciousness to that of a mindless servant. This allowed aboleths to keep slaves, known as aboleth servitors, which they dominated and kept captive through their mind. Only the most powerful aboleths could do this, however, completing the process through a powerful ritual.
Another strange feature of aboleths was their memory. An aboleth was born with a racial memory, each individual inheriting the memories of its ancestors. Furthermore, it assimilated the memories of those it consumed. Each aboleth's memories were stored within an ever-growing part of its brain that extended down its back as it aged. Aboleths enjoyed spending time lost in particularly fine memories of their ancestors, and if they had nothing better to do, they might relive entire portions of their forebears' lives.
Aboleths were all hermaphroditic, possessing both male and female reproductive organs. When aboleths bred, they did so in private, laying roughly three to nine eggs once every five years. When laid, the eggs gestated for the same five years before hatching into fully functional aboleths. Although these young aboleths were, for all intents and purposes, adults in all but size, they typically remained with their parent for roughly a decade, obeying the elder aboleth without question before setting out on their own. 
Aboleths were both extremely cruel and highly intelligent. As a result, they were among the most dangerous foes that existed in the multiverse. Holders of many terrible secrets thanks to their unique racial memory, aboleths were born fully aware and with all the memories of their ancestors, making even the youngest aboleth a frighteningly deadly predator. They were well aware of their weaknesses, however, and would not attack land-bound foes if they considered it to their disadvantage.
Aboleths were utterly self-centered as a race; they knew they were among the first beings in existence, and saw all things as theirs, having a particular loathing for land-dwelling creatures. Their enmity towards other races stemmed in part from their perception that these "upstart" races had stolen what was rightfully the aboleths'. All that stopped them from conquering the surface was their weakness on land (though an aboleth was always a fierce opponent) and the fact that they would rather enjoy themselves than waste time subduing feeble creatures such as humans. By contrast, they were greatly unsettled by the similarly powerful mind flayers, in part because they lacked knowledge of the race's precise origins.
Wholly alien but dangerously intelligent, aboleths were among the most powerful creatures in all of the known multiverse and, although often removed from human affairs, they did not hesitate at any point to kill or use any unfortunate mortals who crossed their path.
Aboleth society was utterly alien in many ways to that of more familiar races, in part due to the racial memory all aboleths exhibited as well as their generally bizarre psyches. Some aboleths formed clusters known as "broods", ruled over by powerful "overseers." These broods were often accompanied by aboleth servitors or other minions, such as the kuo-toa who were known to sometimes serve the race. 
Aboleths had no gods that they worshiped. While they acknowledged the presence and power of gods, they had memories of a time long before any modern gods were worshiped and recalled such gods' birth and often demises within their own lifetimes. They were not concerned with an afterlife since their perspective on death was to consider it a failure and they intended to live forever. Aboleths did, however, have a certain respect that sometimes approached reverence for the powerful beings known as elder evils.
Aboleths used the term boorm (meaning "flow") to indicate a period of time.
Like most aberrant creatures, aboleths were originally from the Far Realm, though long ago many of them emigrated from the distant plane to the Prime Material Plane, where they settled in the Underdark. There, the vast majority of Toril's aboleths dwelled, though they could be found elsewhere, most commonly haunting ruins, deep lakes, or old temples. In some of these places, the kuo-toa foolishly served them.
Aboleth cities were vast affairs of bizarre and alien architecture, located deep underwater. The Shape of Water, located in the Underdark's Glimmersea, was the largest known aboleth city and was the main place the leaders of the race resided and held council.
Aboleths originally came to Toril when the world was young. The ancient obelisk-shaped city of Xxiphu plummeted to the world and settled deep in the earth's crust, below what was later the Sea of Fallen Stars. The oldest known aboleth and possibly the progenitor of the entire species, the Eldest, was an enormous creature that rested atop the city like a throne. The ancient aboleths of Xxiphu formed an organization called the Abolethic Sovereignty. Before 1479 DR, they were roused from a period of hibernation that spanned millennia, and the city of Xxiphu rose above the Sea of Fallen Stars and conquered territory for the Sovereignty.
- The Eldest
- Ruler of Xxiphu and the Abolethic Sovereignty.
- Ruler of Zanhoriloch.
- An aboleth of Zanhoriloch who was consumed by Oothoon.
- ↑ 1.0 1.1 1.2 1.3 Wizards RPG Team (2014). Monster Manual 5th edition. (Wizards of the Coast), p. 13. ISBN 978-0786965614.
- ↑ 2.0 2.1 2.2 Mike Mearls, Stephen Schubert, James Wyatt (June 2008). Monster Manual 4th edition. (Wizards of the Coast), p. 8. ISBN 978-0-7869-4852-9.
- ↑ 3.0 3.1 3.2 3.3 3.4 3.5 Skip Williams, Jonathan Tweet, Monte Cook (July 2003). Monster Manual 3.5. (Wizards of the Coast), p. 8–9. ISBN 0-7869-2893-X.
- ↑ Bruce R. Cordell (April 2004). Expanded Psionics Handbook. (Wizards of the Coast), p. 185. ISBN 0-7869-3301-1.
- ↑ 5.0 5.1 5.2 5.3 Eric L. Boyd (1999). Drizzt Do'Urden's Guide to the Underdark. (TSR, Inc), p. 12–14. ISBN 0-7869-1509-9.
- ↑ 6.0 6.1 6.2 6.3 Skip Williams, Jonathan Tweet, Monte Cook (July 2003). Monster Manual 3.5. (Wizards of the Coast), p. 8. ISBN 0-7869-2893-X.
- ↑ 7.0 7.1 7.2 7.3 7.4 7.5 Skip Williams, Jonathan Tweet and Monte Cook (October 2000). Monster Manual 3rd edition. (Wizards of the Coast), p. 15. ISBN 0-7869-1552-1.
- ↑ Lisa Smedman (February 2005). Extinction. (Wizards of the Coast), p. 206. ISBN 0-7869-3596-0.
- ↑ 9.0 9.1 9.2 Richard Baker, James Jacobs, and Steve Winter (April 2005). Lords of Madness: The Book of Aberrations. (Wizards of the Coast), p. 17. ISBN 0-7869-3657-6.
- ↑ 10.0 10.1 10.2 Mike Mearls, Stephen Schubert, James Wyatt (June 2008). Monster Manual 4th edition. (Wizards of the Coast), p. 8. ISBN 978-0-7869-4852-9.
- ↑ Mike Mearls, Stephen Schubert, James Wyatt (June 2008). Monster Manual 4th edition. (Wizards of the Coast), pp. 8–9. ISBN 978-0-7869-4852-9.
- ↑ Lisa Smedman (February 2005). Extinction. (Wizards of the Coast), pp. 117–118. ISBN 0-7869-3596-0.
- ↑ Bruce R. Cordell (2009). City of Torment. (Wizards of the Coast). ISBN 978-07869-5184-0.
- ↑ Bruce R. Cordell, Ed Greenwood, Chris Sims (August 2008). Forgotten Realms Campaign Guide. (Wizards of the Coast). ISBN 978-0-7869-4924-3.
- ↑ Bruce R. Cordell (December 2008). Plague of Spells (Mass Market Paperback). (Wizards of the Coast), p. 162. ISBN 978-0-7869-4965-6.
- ↑ Lisa Smedman (February 2005). Extinction. (Wizards of the Coast), p. 117. ISBN 0-7869-3596-0.
- ↑ Lisa Smedman (February 2005). Extinction. (Wizards of the Coast), p. 169. ISBN 0-7869-3596-0.
- Richard Baker, James Jacobs, and Steve Winter (April 2005). Lords of Madness: The Book of Aberrations. (Wizards of the Coast). ISBN 0-7869-3657-6.
- Wolfgang Baur (October 1995). “Secrets of the Sunless Seas”. In Pierce B. Watters ed. Dragon #222 (TSR, Inc.), pp. 90–94.
- David "Zeb" Cook, et al. (1989). Monstrous Compendium Volume Two. (TSR, Inc). ISBN 0-8803-8753-X.
- Ed Bonny, Jeff Grubb, Rich Redman, Skip Williams, Steve Winter (September 2002). Monster Manual II 3rd edition. (Wizards of the Coast). ISBN 0-7869-2873-5.