Fortunately Fimm Mc Cool was on hand to supply a potted history of the Fimir:
"Millennia ago, before humans, before even elves and dwarves, this world was very different. Much of it was covered with shifting quagmire and swamp, inhabited by reptilian animals and crude life forms. Into this rich source of life came the Great Old Ones. They had fled their world, which was being consumed by the ravages of chaos, unleashed by the Old Ones’ experiments in warp-gate technology, and were seeking a new home. Little did they realise how soon the cycle would repeat itself.
The Old Ones had enormous minds, they were great wizards and cunning artificers and they set about shaping the world to their whim and forming intelligent life to instruct as servants. Their first experiments with the reptilian beasts were unpromising, but then they had a breakthrough combining reptilian and amphibian forms and created bipedal, tough, intelligent creatures, sallow of skin and with a single eye and prehensile digits. The Old Ones taught them craft and instructed them in the ways of nature and initially it seemed this servant race was a success. As the centuries passed and their drones grew in wisdom (they were long-lived, some passing a thousand years in age) they noticed a change. Their creatures were becoming more independent, longing for freedom and beginning to form their own ideas, opinions and theories about their masters. The Old Ones realised that nurturing a race into knowing submissive servitude was heading for disaster and so the spawning process stopped. No more were created. The Old Ones had bred the race to be unable to reproduce naturally, ensuring that every creature produced was male, and so when they stopped the programme the doom of the species was sealed... or so they thought. The attention of the Old Ones turned to further experiments, eventually raising the lizardmen in a similar fashion, and then the elves and dwarves as privileged children, keeping them servile by love, not enforced obedience. Their original creations they cast adrift to wander until death in the forming wilderness of the world.
There was one of the Old Ones whose name was Balor. He was accounted among the most powerful of the race and was appointed as sentinel of the northern warp-gate and tasked to watch there day and night without rest, as such he was prevented from taking part in the creative shaping that engaged the rest of the Old Ones. Balor had a single eye in the front of his face, which he turned towards the warp. This eye never closed, never blinking or in sleep, and its direct gaze was death to any enemy he looked upon. In the back of his head he had another eye, so that he was still aware of the goings-on in the world he guarded. As the first-born of the Old Ones wandered northward Balor took pity on them. One-eyed himself, at least to their world, and denied the creative pleasure of offspring he saw in them an echo of himself and adopted them as his children, appointing them earthly guardians and servants of the northern gate. He named them ‘Formorii’, or ‘orphans’ and would accept no other servants sent by the Old Ones.
The Formorii loved Balor and served him without reticence as the years wore on, but their population was ageing and with no replacements the extinction of their species seemed imminent, and it was here that Balor erred. Maybe exposure to the stuff of the warp had twisted his judgement. Maybe the denial of a chance to create had made him over bold, maybe his love for the Formorii overcame his moral standing. Whatever the cause, Balor held captive members of a detachment of elves, primitive forms, not elves as we know them, which had been sent on an errand by the other Old Ones. And Balor instructed a handful of hand-picked Formorii how to interbreed with the elves. When the other Old Ones heard what their kinsman had done they were outraged and sent out a great army to destroy the Formorii, but Balor turned his body and gazed upon them with his dreadful eye and they were destroyed, and the north of the world burned to a charred wasteland. The moment of Balor’s turning was instantaneous, but it was enough for an entity of chaos, which had been lurking in the warp beyond, to creep into the world. No doubt Balor intended the creation of a new generation of Formorii to be an occasional event, or even one of a kind in order to produce females for the rest of the race, but this chaotic force latched onto their consciousnesses and awoke in them a terrible lust. Today, some may call this entity Slaanesh.
Seeing his children changed, Balor watched them ever more intently. Whenever a group would go abroad to try and find captives of other species for their own twisted breeding experiments he would turn his deadly eye upon them, and yet the urges that had been awakened in a race so long forced to undergo celibacy were strong. Balor’s intent gaze rendered the entire race very sensitive to light and so they began to shun daylight, preferring to move abroad by night, though even this did not deter Balor’s stare. As his attention focussed more on his errant children the forces of chaos mustered behind the warp-gates. And without the full attention of their guardian and the maintenance work of the Formorii, the gates fell. Chaos entered the world.
The Formorii fled to caves and wastelands across the north of the world, many were destroyed but those who had the awakening of Slaanesh within them were spared the destruction and survived the first incursion. When they emerged they had grown in strength and determination for the continuance of their race, striking deals with the lords of the warp for continued existence. Seeking to keep them in line the forces of chaos twisted their genetic makeup, radically decreasing the possibilities of producing female children, forcing them to continue their degenerate rampage in order to survive. They gave themselves a new name, the Fimir, or ‘adopted’, in a foul irony. They believed, for the most part, that Balor had, n fact, stepped aside to allow chaos through, bringing righteous retribution to the Old Ones who had denied them life and vindicating the behaviour of the Fimir. During this period the race mutated, producing five strains of creature which gave rise to a hierarchy based on physical and magical power. The lowest and weakest were the Shearl, quickly pressed into service as the Formorii had been of old. The most common retained the physical characteristics of the Formorii, albeit now infused with the daemonic, and were named the Fimm. The Mistmor stood taller and stronger than the Fimm, and initially retained intelligence, yet with the generations their cognitive ability dimmed and failed, a victim of warped mutation. The Dirach were the result of those Fimir who walked most closely with the daemons, possibly even interbreeding with them at times. They were as tall as Mistmor, horned and possessed of terrible magical ability. Some female Fimir were born despite the attempts of chaos to prevent them. These grew against strong oppression and soon became forged by tribulation into the most powerful of the Fimir. The Mearghs, as they became known, were even more powerful wizards than the Dirach, maybe the intervention of chaos leaked more magic into their blood than intended, and soon began to draw other Fimir in bands around them. They were proud and would not tolerate competition, nor would they accept the advances of Fimir males they considered inferior, and so over time grew sterile.
For all their allegiances with chaos and attempts to repopulate, the Fimir were decreasing in number. Elves had withdrawn from the extremities of the world (which they had only ventured into in service to the Old Ones, now disappeared) and attempts to interbreed with dwarves and even animals had proven unsuccessful. As their race waned once more one of the most powerful of the Meargh called for a united front. Her name was Annun and she had a plan. Annun’s clan lived in the far north of what is now Albion, in a fortress built of black granite and named Khulaine. Within this fortress, suspended over a great shaft at the heart of the castle, was a crystal, last remaining piece of the warp gates. Annun claimed that through this crystal, Balor spoke to her of a glorious future for his people. Balor’s act in stepping aside at the gate had earned him the high privilege of becoming one with the warp and even now his very life force was flowing through the magical essence in every Fimir. By learning to listen to his urging the Fimir would establish their race and subdue the world that had rejected them. In a little over two centuries the whole remainder of the Fimir clans had grouped around the crystal. Hostility was rife, especially among the Meargh who resented any who claimed authority over them, and a civil war threatened to break out. Annun summoned the clan leaders to a contest. Whoever could break a piece from the crystal would demonstrate they had the blessing of Balor to lead his people to triumph. Each Meargh was to take in turns to strike the stone, whoever broke a piece off would be crowned queen of the Fimir. Annun herself went first, but for days the Meargh struck without success. Then, as evening drew in on the fifth day, a hit from a Meargh named Morrigû shattered a piece from the side of the crystal. Yet the Fimir had not expected what happened next. Pure warp essence, enshrined within the stone which had powered the gates of the Old Ones, flooded the castle. The Fimir were engulfed in a wave of something not experienced before or afterward. All memory of what happened is lost, but it appears the entire race of the Fimir slept, enshrined in the castle, for five thousand years. During these years it is believed Balor spoke to each individually, setting a task for each clan and each individual to perform.
When they finally awoke, the world outside was much changed, as were the Fimir themselves. Numb, they staggered out of the castle to behold a world populated with new species. Factions divided, each claiming a different view of their situation. Some claimed this was punishment for marring the stone, new races would fulfil the role the Fimir were to have played. Others declared these new creatures were rich pickings provided by Balor. A fierce battle broke out and the Fimir drifted their separate ways away from the castle. Few survived the slaughter or the following decades in the radically changed climate. By far the largest clan to be lead away from Khulaine was headed by Morrigû herself, still clutching the piece of hewn crystal. Legend says that Morrigû was chosen to be the mother of the Fimir species, and so, probably alone of the race, she encouraged the birth of daughters who she taught and equipped to become clan leaders and form their own tribes as offshoots. Those recorded of her children are Fea, Neman, Badb and Macha. It is rumoured these clans keep strong ties and will aid each other if need arises, a rare claim for Fimir tribes.
In the Old World, the tale of the Fimir picks up again in a region known as the ‘Waterland’, where a Fimir, possibly a Dirach, calling himself Fimul courted and sired offspring with a woman named Maris. Whether this was a romantic affair as reported, or merely an idealised telling of yet another case of abduction and rape is open to debate. My source would not confirm or deny this legend, declaring it only to be a ‘possibility’. If true it would explain resurgence in Fimir activity, one which has since declined. My source believes that the time is drawing near when all things spoken of by Balor in the ‘dreaming’ are coming to fulfilment, soon the crystal will call to the Fimir to return to Khulaine once more for the reckoning. Indeed, some may already have felt the call."