The Great Horned Rat is the fifth Chaos God, rising to join the pantheon in the last days of the world. The Horned Rat's origins can be traced back to the World Before Time, with the creation of his people thanks to the toiling of an unnamed mortal clad in grey. His work -- the creation of a Screaming Bell -- brought an entire city low and destroyed not only its Human and Dwarfish citizens, but also created the Skaven -- the end product of both mundane rats and the Human children of the city being exposed to the mutating effects of Warpstone.
With the fall of the mortals, the Skaven proceeded unopposed to overtake the city's subterranean ruins, which were dubbed Skavenblight. The Skaven first became aware of the Horned Rat's existence following a failed attempt to expand their already substantial home -- some unforeseen wrench in the works of a great tunneling machine destroyed every building in Skavenblight, save for one -- the large church in the centre of the city's ruins that housed the first Screaming Bell.
From the church, those Skaven that had survived watched as twelve grey-furred rodents stepped out, who proceeded to explain that were the ones who had been chosen by the Horned Rat to lead their people, as ordained by their scabrous new deity.
Since then, the great Horned Rat has served as the symbolic leader of the Council of Thirteen -- the Skaven's twelve most powerful leaders, with the Great Horned Rat claiming seat 13, the most powerful spot on the council.
Unbeknownst to the Skaven, the Horned Rat has much more of an active role its children's lives than they realised -- just not as expected. The Great Horned Rat serves on a second council -- the Shadow Council of Thirteen, forged of itself and the Verminlords -- rat daemons and deities alike for the Skaven -- of the twelve main clans of the Skaven.
For the most part, the Great Horned Rat stays in the shadows, watching its children quarrel with one another, sabotage other species and cause general mayhem in the Mortal Realms. However, on rare occasions, the Great Horned Rat will deem it necessary to personally interfere in the affairs of mortals.
This has usually occurred whenever a Skaven civil war has gotten out of hand; this has only occurred twice, but the restoration of the Skaven as a species could mean its presence will be more keenly felt.
Recently, the Great Horned Rat has been able to ascend into the pantheon of the Chaos Gods; though regarded as a lesser deity by his peers, it's only a matter of time until it becomes as dangerous as the other Dark Gods.
While the skaven view their god with some commonalities, he is also viewed and even named differently from clan to clan. These variances can be wildly different, though tend to be consistent with the main theme of the Skaven Clan in question. For instance, Clan Verminus views the Great Horned Rat as being a warlike being who demands his worshippers rend his enemies to peices with tooth and claw and refer to him as the Great Conqueror or the King of Lashes. Clan Pestilens views him as the Great Corruptor, the master of disease and virulence. Clan Skryre refers to him as the Dark Innovator and imagine him as a twisted mechanical beast for whom they twist and re-purpose the technologies in the world. Clan Moulder calls him their Writhing Broodsire and Fleshgifter, imagining him as a heavy mass of ratflesh. Finally, Clan Eshin refers to the Horned Rat as the Murder Shadow or Scuttler-in-the-Dark who brings low kings, lords and champions.
The Grey Seers have their own secret names for their god, thirteen names specifically, that is known only among their order.
Ambitions and Mythology
"The other gods underestimate the Great Horned Rat...at their own Peril."
- — Skaven Battletome
The Great Horned Rat is a minor Chaos god, paranoid and abominable. He seeks ruination of the mortal realms, not just for it's own sake, but rather to gain primacy amongst the other Chaos gods. Viewing them as rivals, he believes the elimination of their worshippers will render them weak and therefore set the stage for the Horned One himself to become paramount of the pantheon. To this end, he uses his children to visit destruction of all surface-dweller societies. However, his love of ruin is not limited to his enemies; The Great Horned rat also enjoys watching his children tear each other apart, enact scheme after scheme, commit atrocity after atrocity.
But in true skaven fashion, this skaven-on-skaven conflict also has a purpose and isn't merely for enjoyment. The Horned Rat has so primed the minds of his children that the society they create is brutal and merciless. Only the most depraved, cunning, and deadly of the ratmen can survive let along thrive. The weak are disallowed to breed, are worked until death, and barely survive day to day and this is of the Horned One's devising. He believes the veritable testing ground that is skaven society will only make the skaven stronger as an ultimate result and therefore more able to carry out the Great Ascendancy.
- [Skaven Battletome Prologue V] ( "In the last days of the world-that-was, a fifth deity rose to join [the] dark Pantheon of the Chaos Gods.
- Skaven Battletome, Page 4,5,6