The Abyssal are the mad followers of the mad Akylios, who was driven insane eons ago. They are the hoarders of all knowledge dark and twisted, always seeking answers to hideous and profane secrets. They form cabals of insane priests and Tidelords, claiming to hold the promise of the world's knowledge if only the unenlightened would look far enough and deep enough into the crushing deep of the Abyss that Akylios represents. They are a tight-knit, extremely secular cult made up of different cabals or 'cells' within the cult. Each cell is headed by a Tidelord, who conducts the business and direction of each cell differently from the others. Even though they are all part of a whole and acting toward an overall common goal, each cabal has it's own separate goals and desires as well, with each Tidelord seeking his or her own knowledge and secrets of the dark. Since each cabal is completely separate and located in different parts of the world, if one falls, it is nearly impossible to trace it to another cabal. And thus the Abyssal are the hardest to discover and unearth among the citizens of Telara, since they are very good at pretending to be ordinary, innocent Telarans. They are adept at infiltrating a village and replacing the villagers with their own followers, converting and killing where it's needed in order to accomplish their goals. They are swift to violence, unpredictable, and are powerful casters. They act more for their own desire for power and profane knowledge rather than because of a sound plan of attack or an organized battle strategy.
The leader of the Abyssal Cult, Tidelord Jornaru, can be found plotting against the Ascended in Abyssal Precipice and in Hammerknell Fortress, striving always to free his lord and master, the great Akylios.
Another famous member of the Abyssal is the Faceless Man, who is now the leader of the Unseen, a group of assassins and spies in Meridian who protect the Defiants secrets and work to bring information to and from the Defiant headquarters in order to best deal with the threats to Telara. The Faceless Man was once a Tidelord of an Abyssal cult that controlled areas of Freemarch before he betrayed his dark master to the Defiant.
The Abyssal Cult are all quite insane, driven mad by their burning desire to unearth the dark secrets of the worlds. To try to understand the innermost workings of the Abyssal is to court madness yourself. No culture or race is exempt from these mad cultists, who come from all manner of place and status. Compared to the other cults and followers of the Blood Storm gods, the Abyssal contain the most scholars, magi, academics, and professors of the arcane arts.
Rank among the Abyssal is dependent upon one's individual knowledge, power, and level of insanity, rather than status in Telara. The Tidelord leaders are all recognizable by the distinctive horned helmets that cover the face. The helmets hide the disfigurement they voluntarily undergo in order to better 'see' the deeper knowledge that Akylios grants them. The ritual to become a Tidelord is an arduous task that only the most faithful, and the most insane, undergo. They give up their names, their memories, their very identities, to better serve Akylios, who promises greater arcane and eldritch knowledge in return for such devotion. He delights in the madness of others, and the more insane, the better. In return, the Abyssal cultists gain mad genius and knowledge best left forgotten in the depths. The more knowledge they gain, the further they fall into insanity. And thus the Abyssal have the reputation of being the most secretive, but also the most incomprehensible dragon cult. Their tomes and scrolls, if found by an unsuspecting person, can lead to madness and death just as easily as enlightenment or power. Or both.
They seek neither treasure, wealth, or fame, nor power for its own sake, but wish only to learn. To learn everything that the dark Abyss can teach them and beyond. To gain the secret powers of the hidden arts. The one uniting force that drives the Abyssal other than the desire for knowledge is the desire to free Akylios from his watery prison, where he lays dreaming beneath Hammerknell Fortress. Many nests of the cult have apparently wormed their way into the outskirts of Telaran society, setting up shop in rural villages and disguising themselves as professors of arcane knowledge or traveling scholars. They undermine the efforts of the Ascended, convert others to their cause, and always seek ways of freeing Akylios. They readily interact with and ally with the riftspawn that come through the rifts, summoning Deep Ones, Fathomlords, profane many-eyed monsters and other planar ilk to do their bidding guard their secrets. The Abyssal are the ultimate Lovecraftian model in Rift, with themes of madness, desire, knowledge, unfathomable secrets, insanity, cabals of arcane practitioners and themes of water, nightmares, tides, darkness, and the Abyss. By the time one figures out that the knowledge and answers they sought lead to nothing but darkness and insanity, it is far too late to turn back.
Despite their evident insanity and warped minds, don't underestimate the Abyssal cult and its insane leaders, because the clarity that madness brings can be just as effective and deadly as a sound battle strategy.
References: Information on the Abyssal is just as mysterious as the cult itself, and hard to verify. A lot of this was learned by talking to the Faceless Man and reading through clues in quests and artifact sets. The names of leaders was found in the Abyssal Precipice dungeon and by combing through the forums! All information is not mine, I'm just writing it for my own purposes since there's so little actual intel on Rift and its lore.