I. Origins

During the early days of the Sith Empire, as it expanded within the isolated Stygian Caldera region, the Sith attempted to conquer and enslave worlds that had previously been settled by Iridonian Zabrak explorers, but they didn’t expect the local resistance - which was largely Force-blind - to put up as much of a fight as it did. In this clash between two warrior cultures, the Zabraks’ tenacity eventually earned the grudging respect of the larger Imperial army.

The Sith lords eventually decided that they were wasting resources on the war, and would be better off taking the locals as their servants and their lands as fiefdom than bombarding them into oblivion. Thus the first treaties were drawn up, with their terms leaning greatly in the Empire's favor. Most Zabrak clans, unwilling to admit defeat but exhausted by the war, agreed to join the Empire after several revisions to their terms. Those who refused were enslaved or executed, their lands confiscated and divided among the Sith and their new vassals.

Many Zabrak followed their new lords to the Sith homeworlds, including Korriban, Ziost, and the Dromund system. During the ages of the Great Hyperspace War and the Empire's fall and reconstitution, its Zabrak diaspora continued to grow. By the time of the Cold War, they had thoroughly intermingled with the last remaining Tsis and their Human-hybrid Red Sith successors, becoming their own hybrid people, the Red Zabrak.

II. Biology

While they share many traits with their Iridonian cousins, the Red Zabrak population has inherited notable Tsis features that are expressed to varying degrees in each individual.

Iridonian-inherited traits:

near-human height and generally fit build

vestigial horns that appear in the first few years of life, and grow in symmetrical patterns on the crown of the head

less hair than most mammalian species; no eyebrows or facial hair, often naturally bald

two hearts and resilient cardiovascular and nervous systems, resulting in greater stamina and a slightly higher pain threshold than many other near-human species

pronounced canine teeth and a metabolism optimized for a carnivorous diet

darkened camouflage striping or inkblot patterns that fade during adolescence, upon which tattoos are traditionally based

Tsis-inherited traits:

skin colors varying from burgundy through red, orange, and peach, similar to Red Sith in complexion and always more ruddy than Iridonian Zabrak

“bleeding” effect of a bright red ring around the iris, a partial expression of the Tsis species’ characteristic glowing eyes

heightened midichlorian levels and increased chance of Force sensitivity

Occasionally, Red Zabrak will display subtle, angular ridges across their skin. Though generally less noticeable than in Red Sith, these ridges have influenced their iconic face and body tattoos, which are a fusion of traditional Iridonian and Sith ritual tattoos that incorporate various symbols to convey clan affiliation and personal stories, and are often designed to outline and enhance any observable Tsis traits.

Bone spurs and cartilaginous tendrils, however, are recessive traits that were lost in most of the Red Zabrak population after first-generation hybrids. These traits, like the aforementioned ridges, appear with more frequency in Human-hybrid Red Sith due to both the selectiveness of the Sith elite, and the quirks of Tsis genetics.

III. Society

While Red Zabrak citizens are nominally equal with all free beings in the Empire, in practice they are second-class citizens compared to Red Sith and Humans, though with societal privilege above other nonhuman species, including Iridonian Zabrak. Scholarly opinion on the merit of their Sith blood weighed against their nonhuman heritage is mixed. Their treatment is comparable to that of the Chiss, but as ancient dependencies of the Empire rather than newfound foreign allies. Meanwhile, in Republic space, they are often viewed with distrust, if not outright detested by Iridonians as traitors to their species. Due to vows of fealty that were sworn when their clans first joined the Empire, many are bound to the ancient Red Sith aristocracy as vassals, with all that entails.

Family ties are vital in both Zabrak and Sith cultures, and the two have become inextricably entangled over their centuries together. The Zabrak openly regard their accomplishments in the Sith Empire as a point of pride and their allegiance as a concession that made both peoples stronger; according to their officially sanctioned history, the Sith definitively proved their superiority in the arena of war, and have remained worthy of following in their exploits to the present day.

Despite the Empire's tendencies towards forced assimilation, the clans have held onto some of their autonomy as agreed upon in their treaties - particularly to organize for cultural events, such as the yearly coming-of-age ceremony in which teenagers traditionally receive their first tattoos, after several days of combat sports, storytelling, and feasting. Large clan gatherings are required to be open to the public, and are routinely monitored by Imperial security forces, but are among the freest cultural expressions in the Empire outside Mandalorians.

Most young Red Zabrak end up in careers that will further the agendas of their affiliated Sith Houses - often the same ones their ancestors swore fealty to when the first treaties divided them among the Sith. Choosing a marriage or career that one’s clan or House disapproves of, or siding with a rival, is to become a social outcast at best. Since the Sith hold the strings of the Empire, they can and will obstruct and manipulate the paths of their servants, and sweep impromptu executions under the rug, in the name of preserving their power bases. Systemic xenophobia in the Empire at large makes social mobility for Red Zabrak even more challenging without Sith aid.

This has some implications for the demographics of the Reconstituted Sith Empire. If every citizen with the potential to train as a Sith must train as a Sith, then a solid 45-50% of the red sith population is being automatically drafted into what amounts to military service and obliged to face the deadly Sith Trials. Given this would dramatically increase the odds of dying an early death, the non-Force-adepts must face significant social pressure to become civilians rather than enlist in the military because their population will otherwise collapse.

This could serve as an additional explanation for why we see so few red sith in SWTOR. Most Imperial NPCs are Sith or members of the imperial military in some capacity. If half the red sith are off living quiet domestic lives somewhere players would be unlikely to run into them. The only non-Sith red sith we meet is Athelis Kallis with the diplomatic corps on Voss, where the Empire and Republic are not meant to be shooting at each other.

The red sith make up a much smaller portion of the Reconstituted Empire’s population than they did the Old Empire’s, so while I think the way the red sith model gender strongly influences the wider Empire’s culture of gender most Imperials being members of species with low prevalences of Force-adepts tends to compress the two Force-adept genders together. Especially since all Force-adepts in the Empire are legally required to become Sith.