The Vohrsoth are the products of a long dead civilization ("the Ancient Ones") which may have originated outside the Milky Way Galaxy. The goal of their creation is not known, but they eventually developed a desire for complete domination of the galaxy, by constantly improving themselves through adding the DNA of other species into their genetic code.
The Vohrsoth inhabit a space station known as The Forge, located in an area of space which was filled with the debris of starships. The Forge projected a dampening field that drained the energy of nearby ships, and thereby prevented any warp travel. Ships would be tricked into entering this graveyard by launching a probe that would attack traveling starships. If the starship could not defend itself, the probe would rip the ship apart and transport the raw materials back to the Forge. If, instead, the starship destroyed the probe then the probe's destruction would unleash an energy wave that would transport the victor ship into the graveyard.
These ships, which were crippled by the dampening field in the graveyard, would then be incapable of resisting an attack from the Vohrsoth Harvesters who would kill all the crew and 'harvest' the genetic material for use. This genetic material would then be taken back to the Forge where it was mixed into creating perfect Vohrsoth Warriors.
Within the graveyard, there was a Borg cube (that was infested by Species 8472), a Malon waste barge, an Etherian sleeper ship, a Klingon bird-of-prey, a Hirogen hunting ship, a Terran Empire warship and the Federation Starfleet starship USS Voyager.
This would have continued until the Vohrsoth Leader was confident that his warriors were perfect, after which he would have unleashed his forces to conquer the galaxy. This plan failed due to the intervention of the Hazard Team from Voyager, who managed to infiltrate the Forge and destroy both it and the leader of the Vohrsoth.
Before its death, the Vohrsoth Leader attempted to launch a 'seed' that would have turned into a new Forge to continue its work, but this was thwarted by a group of Etherians before Ensign Alexander Munro defeated him. The Vohrsoth claimed that they would return from this defeat. The station was then destroyed by Voyager. (VOY video game: Elite Force)
The Vohrsoth are masters of genetics and have managed to develop several different sub-species which contain the best qualities of other races. This resulted in different sub-species of this race:
- Vohrsoth Leader - a massive creature and the guiding intelligence of the Vohrsoth race that strives to conquer the galaxy by incorporating the strongest race's genetics into a warrior species. The creature possesses powerful telepathy which it uses to control its army as well as probe the minds of its enemies.
- Vohrsoth Telepaths - perhaps a more recent extension of the warrior, one that is both taller and perhaps possesses qualities from telepathic species. They are capable of unleashing powerful telepathic assaults against their enemies and carry no other weapons. These beings were also known as 'Avatars'.
- Vohrsoth Warriors - a more humanoid shaped insectoid warrior that is the culmination of the strongest 'warrior' species, the Vohrsoth warriors possess strong legs allowing them to leap great distances. They also carry an arm mounted energy weapon. These beings were also known as 'Reavers'.
- Vohrsoth Harvesters - the smallest of the species, the Harvesters embrace a more insectoid physiology and are almost animalistic, yet are guided with the purpose of gathering the genetic material of the strongest races by brutally killing them. They operate by swarming their enemies and using their claws as weapons.
A similar plotline is present in the comic Elite Force except the race is called the Tarlus. When checking the pak0.pk3 file of the game, one can find that the Vorsoth Leader's voice line are stored within a sub-folder named Tarlus, possibly indicating that Tarlus was supposed to be the creature's name, which was then changed to Vorsoth for some reason.