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Aboleths are fish-like amphibians of immense size, often reaching twenty feet in length and weighing up to 6,500 pounds, though they continue to grow as they age and some fantastically ancient specimens might reach forty feet in length. They resemble 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 are lamprey-like, filled with serrated, jawless teeth. Aboleth bodies are also segmented, like a worm or insect.
Aboleth underbellies are often orange-pink, while their topsides are typically sea-green. A little bit back from the head are four long tentacles, two sprout from across each other on the top, and two more of the same 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. Aboleth blood is green and thick, oozing like sap.
Aboleths breathe through a thick gray mucus-like substance, which covers their body and which they extrude from four pulsating organs along their body as they move.  If robbed of the ability to extrude this slime, an aboleth will suffocate in water or on land alike. As such, an aboleth must take care of its mucus. Out of the water, an aboleth's membrane-like skin dries out quickly, but this does not prove fatal in and of itself. Instead, the aboleth will 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 forms a tough, waterproof membrane. However, if this membrane is pierced, liquid floods out and death is usually not far off for the aboleth.
Aboleths do not die of old age and so live on indefinitely barring violence or disease.
Aboleths have powerful psionic powers and are natural psions like mind flayers and many other denizens of the Far Realm. However, aboleths have a much more fearsome ability, the capacity to secrete a viscous gray fluid, much like mucus, which brings about a terrible transformation in air-breathing creatures so unfortunate as to be caught in the stuff. The skin of the victim is transformed into a membrane which allows it to breathe in water, and changes the creatures consciousness to that of a mindless servant's. This allows aboleths to keep slaves, known as aboleth servitors, which they dominate and keep captive through their mind. Only the most powerful aboleths can do this, however, completing the process through a powerful ritual.
Another strange feature of aboleths is their memory. An aboleth is born with a racial memory, each individual inheriting the memories of its ancestors. Furthermore, it assimilates the memories of those it consumes. Each aboleth's memories are stored within an ever-growing part of its brain which extends down its back as it ages. Aboleths enjoy spending time lost in particularly fine memories of their ancestors, and if they have nothing better to do, they may relive entire portions of their forebears' lives.
Aboleths are all hermaphroditic, possessing both male and female reproductive organs. When aboleths breed, they do so in private, laying roughly three to nine eggs once every five years. When laid, the eggs gestate for the same five years before hatching into fully-functional aboleths. Although these young aboleths are, for all intents and purposes, adults in all but size, they typically remain with their parent for roughly a decade, obeying the elder aboleth without question before setting out on their own. 
Aboleths are both extremely cruel and highly intelligent. As a result, they are among the most dangerous foes that exist in the multiverse. Holders of many terrible secrets due to their unique racial memory, aboleths are born fully aware and with all the memories of their ancestors, making even the youngest aboleth a frighteningly deadly predator. They are well aware of their weaknesses, however, and will not attack land-bound foes if they consider it to their disadvantage.
Aboleths are utterly self-centered as a race; they know they were among the first beings in existence, and see all else as theirs, having a particular loathing for land-dwelling creatures. Their enmity towards other races stems in part from their perception that these "upstart" races have stolen what is rightfully the aboleths'. All that stops them from conquering the surface is their weakness on land (though an aboleth is 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 are greatly unsettled by the similarly powerful mind flayers, in part because they lack knowledge of the race's precise origins.
Wholly alien but dangerously intelligent, aboleths are among the most powerful creatures in all of the known multiverse and, although often removed from human affairs, do not hesitate at any point to kill or use any unfortunate mortals who cross their path.
Aboleth society is utterly alien in many ways to that of more familiar races, in part due to the racial memory all aboleths exhibit as well as their generally bizarre psyche. Some aboleths form clusters known as broods, ruled over by powerful "overseers." These broods are often accompanied by aboleth servitors or other minions, such as the kuo-toa who are known to sometimes serve the race. 
Aboleths have no gods that they worship. While they acknowledge the presence and power of gods, they have memories of a time long before any modern gods were worshiped and recall such gods' birth and often demise within their own lifetimes. They are not concerned with an afterlife since their perspective on death is to consider it a failure and they intend to live forever. Aboleths do, however, have a certain respect that sometimes approaches reverence for the powerful beings known as elder evils.
Aboleths use the term boorm (meaning "flow") to indicate a period of time.
Like most aberrant creatures, aboleths are 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 dwell, though they can be found elsewhere, most commonly haunting ruins, deep lakes, or old temples. In some of these places the kuo-toa foolishly serve them.
Aboleth cities are vast affairs of bizarre and alien architecture, located deep underwater. The Shape of Water, located in the Underdark's Glimmersea, is the largest known aboleth city and is the main place the leaders of the race reside and hold 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 is now the Sea of Fallen Stars. The oldest known aboleth and possibly the progenitor of the entire species, the Eldest, is an enormous creature that rests atop the city like a throne. The ancient aboleths of Xxiphu form an organization called the Abolethic Sovereignty; they were recently roused from a period of hibernation that spanned millennia, and the city of Xxiphu has since risen 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.
- ↑ 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.
- ↑ Cite error: Invalid
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- ↑ 7.0 7.1 7.2 7.3 Skip Williams, Jonathan Tweet, Monte Cook (July 2003). Monster Manual 3.5. (Wizards of the Coast), p. 8. ISBN 0-7869-2893-X.
- ↑ 8.0 8.1 8.2 8.3 8.4 8.5 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.
- ↑ 10.0 10.1 10.2 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.
- ↑ 11.0 11.1 11.2 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.