They are a Xenos race confined to 3 worlds in the Fidea system and mortal enemies of the Fidea Imperial Guard especially the 44th Fidea as such most of the information the Imperium has on this race came after the death of the commander for whom the species is named in 723 M41.(the name by which they call themselves is unprouncable)
Once confined to the frozen world of Fidea Secundus they began a nascent space program sometime in M31 to escape only to discover that the worlds of Fidea III and IV were just as uninhabitable.
Undeterred and reasoning that since they had survived one frozen world they could adapt to the others easily, they built cities underground to escape the cold. These cities would go unnoticed for 10,000 years as the people of Fidea Prime were trying to survive an ice age. Among the rulers of the species, still living on Fidea Secundus these other settlements would become known as the "Lost Colonies" and would remain so until contact was reestablished with them almost 8000 years later.
History of the Wel'Kor'Cha
They could hardly fail to notice when an Imperial Warship entered the Fidea system. However they thought nothing of it, they once had spacecraft but had written them off as a bad idea when the Lost Colonies were lost. This warship, only arriving in the system due to an act of sabotage by 500 crewmen who had turned to Chaos to cope with their cruel commander, would go on to discover Fidea Prime and bring the people of Fidea into the Imperial fold, all unknown to the Wel'Kor'Cha.
Teodora Mafetti captain of the Battlefleet Medici cruiser Leonara Superba exiled the 500 to the surface of Fidea Secundus believing that the weather would kill them quickly. He was wrong.
Wel'Kor'Cha hunting parties brought the 500 before the ruler and his court. It was here that the hatred between human and Wel'Kor'cha began. These renegades regaled the monarch with a distorted version of the Horus Heresy and all of the Imperial cruelties that followed, however they failed to mention just how large the Imperium truly was, these ideas also failed to translate as the Psykers had never before read a human mind and were unused to the experience. The monarch, the higher nobility and the warrior class turned to Chaos undivided shortly thereafter blending it with their own religious traditions.
Spurred on by the word of Khorne, the ruler and his warriors went on a decades long campaign and crushed the "Freeholds"-led by warlords who denied his authority, uniting their world under the 8 pointed star of Chaos. The 500 would die in the intervening decades, providing knowledge and technology and they would come to be regarded as holy figures, prophets of a sort.
The Wel'Kor'Cha would not be a united people until late in M41 when the current rulers, having recently relearned spaceflight, improved by the knowledge brought by The 500 finally reestablished contact with the "Lost Colonies" all while the Imperium took no notice. Millenia 41 saw them finally take notice of Fidea Prime. Recognizing it as an Imperial World the united armies- led by the Supreme Commander Wel'Kor' Cha invaded Fidea Prime in 690.
Their grievous errors in strength and numbers, they attacked Fidea with no more than 250,000 soldiers against an entire world, saw them driven back and led to decades of war sometimes gaining great victories, and sometimes terrible losses.
But the war was an oddly small scale event compared to the other wars won by the Imperium, the roughly 95000 men of the Fidea Imperial Guard never faced more than a few hundred thousand Wel'Kor'Cha at a time. But both sides constantly reinforced their field armies.
They eventually lost in 723, Wel'Kor'cha died in battle and they were reduced to remnant populations actively hunted by the Fidea Imperial Guard.
Similar to humans in size and average strength they are better adapted to cold than humans,with a thick fur coat. and stunted facial features which exposes less to the cold, however this only does so much, they still wear protective clothes. They are likely descended from the shaggy porcine creatures that wander Fidea 2 and so they also possess a pair of tusks. Like humans they possess 2 arms and legs but their hands and feet end in claws. Also unlike humans multiple births are the norm typically 4 or 5 at a time. This has lead to a superstition among them that only children or twins are unlucky unless they are born as Psykers(see below)
Rulers and Nobles
The highest class of their society, the rulers were always male. The nobles served as military commanders with members of the warrior class serving as their subordinates in the field. Nobles of both genders also served as governors of cities and territories, and if the ruler failed to produce a male heir, the closest male relative would take his place as ruler.
Being a ruler or a noble could be dangerous, constant power struggles took place among those devoted to Tzeentch and madness and bloodshed among those devoted to Khorne.
Not unlike the corrupt rulers of many worlds and species some rulers and nobles were also known to maintain harems of Wel'Kor'Cha females dedicated to Slaanesh- joining such a group was seen as a form of upward mobility for underclass females, some of whom would spend years in training for such a role.
They considered themselves a warrior culture, however they only ever really fought amongst themselves, and most of the time warriors only served to defend the cities from rebellions, unrest and hostile animal life. From M39 onward The single task of warrior class females was to produce the next generation of warriors. Warrior class males were raised almost from birth to be so- never knowing their families or children- their only contact with females came during a yearly event when the warriors were allowed to mate with as many females as they chose.
The elites of the Warrior class served as general staff/bodyguards to the rulers and generals. They were known as the "Black Iron" named for their black iron halberds. Not quite as mad as Khorne Berserkers they were nonetheless devoted to Khorne and possessed of a ruthless bloodthirsty nature, only kept in check by their oaths to serve their masters.
as to their navy- Nobles commanded their ships, while the Underclass served as the crew.
roughly equivalent to the middle/lower class on Imperial worlds- the people who did the work needed to keep society running. Teachers, industrialists, factory workers etc. Chaos worship was not so prominent among them, at least not worship of the 4 chief gods. They tended to place more importance on the 500 who in their eyes urged hard work and the need to strive for better things.
Psykers are rare and revered. They are seen as being blessed by the Chaos Gods and are highly respected as councilors and teachers. Most served the government but a few acted independently in industry and academia- the increase in mental power also provides a massive boost in intelligence and reasoning. Due to their rarity when they are discovered they are instantly regarded as nobles whatever their class of birth and families that gave birth to psykers found themselves with an elevated place in society
They were once led by Wel'Kor'Cha, while the Fidea called him a Warchief his title translated more closely as "He who leads all warriors" - something close to an Imperial Lord General. beyond that organization seemed similar to an Imperial Guard army, with subordinate generals and lesser officers. The internal workings of their lasweapons were based on Imperial designs brought to them by the 500 but they also used their own designs, autorifles and various blades- bladed weapons were seen as being true weapons of Chaos, while other weapons were simply useful tools.
The most common among the average soldier is the Cha'ak Sz'o knife-used for everything from butchering meat to fighting. Their worship of Khorne led them to reckless action time and again and eventually saw them defeated.
Their navy consisted mostly of lightly armed transport ships designed to carry armies over short distances and were never built to face Imperial warships or even the armed merchant vessels converted to warships by the Fidea Imperial Guard
The Wel'Kor'cha worshipped Chaos Undivided to one extent or another, however it was a syncretic religion. They too worshipped the Spirits of their world and their ancestors. As is the way of Chaos it was not an organized religion- each Wel'Kor'cha chose largely on their own which gods and spirits to follow.
The educated tended to follow Tzeentch but beyond that there was no real structure, no clergy- one worshipped through their actions. as noted above some underclass females dedicated themselves to Slaanesh hoping to be chosen by a noble. Whichever combination of gods and spirits they followed they all placed a special reverence on the 500
500 conspirators once exiled to Fidea Secundus they brought the word of Chaos to the Wel'Kor'Cha. They became known as prophets of a sort and upon their deaths now in serve as the guardians of the afterlife and intercessors between them and the Dark Gods. They believe that it is the 500 who will choose who is worthy to join their ancestors in the afterlife and become minor Chaos gods themselves. If the dead are unworthy they will simply cease to exist.