Many millenia ago, the Tarnal Craftworld severed its links with the Webway. The last contact with the Craftworld suggested that some form of mutiny had taken place, with the usual governing structure of Seers and Farseers being replaced by a war-oriented dictatorship.
It emerged that new leader of the Craftworld was an ancient Warp Spider Exarch called Sval. The few inhabitants that escaped through the Webway before all links were severed told of how he was horribly mutated by the Warp.
Sval had become an animal amongst his fellow warriors, but his leadership and sheer aggression won over the hearts of many Eldar onboard. The peace-oriented leadership of the Seers were forced to back down as the whole Craftworld went on a war footing and set course for the Eye of Terror.
Months later the Seers of many other Craftworlds sensed large disturbances in the Warp. The Tarnal Craftworld had crashed headlong into the arms of Chaos in the Eye of Terror and waged war throughout space and on the worlds of daemon princes. The battles must have been of mythical proportions, and the shock waves in the Warp lasted for weeks after the initial battle had been sensed.
However, soon the shock waves died down, and the Tarnal Craftworld was presumed destroyed. The craftworld had been relatively small, and the legend of Sval the Destroyer was forgotten until recently.
In the past hundred years, reports of a strange new breed of aspect warriors were received from many craftworlds. The warriors were first thought to be Warp Spiders, as they jumped across the battlefield in a similar way. However, these warriors were fierce in hand-to-hand combat, and their aggression was unlike the usual Warp Spiders' subtle approach to battle.
The link between these strange warriors and the lost Tarnal Craftworld was not thought of until the battle of Thallus IV.
The remote Exodite world had been attacked by a mighty ork space fleet and had been all but destroyed. City after city had fallen into the hands of the orks, and the exodite world seemed doomed.
The Seers in the capital city of Termallus then sensed a strange disturbance in the Warp, which had previously been filled bye the tremendous power of the Waaargh! In the city streets below them, scores of strange aspect warriors materialised, and they were led by a monstrous being that at first seemed to be some form of daemon.
They watched in amazement as the warriors catapulted forward with a ferocity even greater than that of the ork aggressors. Under the leadership of this daemon they wiped out the entire second wave of ork assault troops.
The ork bosses watched too, in horror, as their front line crumbled in front of them. They quickly ordered a hasty retreat to regroup and build a new offensive.
After the fighting had died down, the strange warriors started to de-materialise as mysteriously as they had appeared, but the daemon instead materialised closeby to Farseer Callamer. The beast stared at him and said, "The scourge has been eliminated .. my work here is done."
Callamer sensed great pain within the monster. Externally it was gruesome, its basically Eldar lower limbs merging into a sinuous and scarred torso, head swollen, and arms mutated into giant pincers. As the beast started to de-materialise, Callamer risked scanning its mind. Pain surged through his body and soul, and he was knocked unconcious.
It was days before he regained conciousness, and when he did he uttered only one word. "Sval."