Ba'ul

The Ba'ul are a sapient, spacefaring species from the planet Kaminar, who share their world with the non-spacefaring Kelpien race.

Very little is known about the Ba'ul, as they're isolationists and tend to remain hidden while using their technological advantage to keep the Kelpiens at bay and pose as superior beings to them. For generations, no Kelpien has even seen a Ba'ul (and lived), so they don't even retain memories of what the species look like.

Biology
What has been seen of the Ba'ul suggests that they're gaunt, aquatic humanoids with spindly limbs and retractable spikes on their back.

Culture and society
The Kelpiens believe that the Ba'ul are predators and that the ecology of their world depends on that which they refer to as the Great Balance. This philosophy is taught to them by the Ba'ul, who are worshiped as superior entities and keep a close eye on the Kelpiens by placing an observation pylon on each Kelpien village, leading them to be collectively known as the "Watchful Eye".

The Kelpiens live a peaceful, idyllic and pastoral existence until they reach the biological process known as vahar'ai. According to their beliefs, vahar'ai signals the approach of death and Kelpiens who reach that point in their lives will willingly offer themselves to the Ba'ul to be harvested as prey. Unbeknownst to them, however, the vahar'ai process actually leads to a physical transformation that turns Kelpiens into their predatory stage, which has evolved to prey upon the Ba'ul.

History
In the past, post-vahar'ai Kelpiens have hunted the Ba'ul to the point of near-extinction, but the Ba'ul managed to resist thanks to their superior technology, which ultimately allowed them to turn the table and resulted in the systematic extermination of post-vahar'ai Kelpiens. In the following eras, the Ba'ul have kept the remaining Kelpiens at bay and controlled every aspect of their cultural development. They made the Kelpiens believe that vahar'ai was death, and that those who pass through it must turn themselves to be harvested to serve the Great Balance.

Appearances

 * Star Trek: Short Treks, s01e03, "The Brightest Star" (2018)
 * Star Trek: Discovery, s02e04, "An Obol for Charon" (2019)
 * Star Trek: Discovery, s02e06, "The Sounds of Thunder" (2019)