Thousands of years before the events of SWTOR, the planet Voss had only one native sentient species, the Gormak. The Gormak are a race of bipedal, tribalistic natives known for being antagonistic to the player characters in SWTOR, much different to the technologically and socially evolved Voss race.

Several millennia ago, a small band of Sith landed on the planet Voss, they were quick to round up the primitive Gormak species and subjugate them to slavery, with only a small group of Gormak managing to escape and form tribes away from the Sith. A small time later, a handful of Jedi explorers arrived on Voss and came into contact with the Elders of these Gormak tribes.

It was discovered that the Gormak species had a strong affinity for the Force. Meaning well, the Jedi taught these Gormak tribes their ways of the Force for use and defence, however the Gormak tribes that the Jedi had taught immediately attacked and killed the Sith that enslaved the other Gormak, which exposed them directly to the Dark Side.
It is unknown what happened to the Jedi that taught the Gormak as they never reported or archived what they had done on Voss before they left or died, leaving the Jedi involvement on this planet a total mystery.

Over the generations, the Gormak tribes that had been taught by the Jedi separated from the rest of the Gormak, viewing them as “lesser” then themselves. The tribes evolved radically in both Force Sensitivity and biologically until they no longer resembled the Gormak they once were.
Climbing the tallest peak on the planet, they established a new society, the Voss.

It was here that they founded Voss-Ka and the Voss turned to their leaders, the “Mystics” for guidance on the administration of their society. However the founding knowledge of how the Voss came to be quickly twisted into legend, with the mythology of the Voss always having existed turned from myth into truth through the following generations.

Clealy influenced and dictated by ancient Jedi teachings and influence, the Voss species relied heavily on their “Mystics” for leadership and often viewed many issues in polarizing light, with conflicts often being boiled down to the “will of the Mystics” through the Force.
To this day the Voss are still readily at arms against the native Gormak, who they still view as savage and lesser to themselves, however after the planet was invaded by the Eternal Empire, both species agreed to a truce at least until the planet would be free.

Sources:

Planet Voss – Star Wars the Old Republic
Codex Entry: Gormak and Voss Origins – Voss
Codex Entry: Voss – Voss
Codex Entry: Voss-Ka – Voss
Codex Entry: Voss-Gormak Alliance – Knights of the Eternal Throne