The Theskians were a humanoid species native to the planet Theskia in either the Alpha or Beta Quadrants. They were described as having blue skin, antennae (which cause extreme pain if bruised), red blood, and yellow fur-like hair. This race was said to be "related" to Andorians, but "more gregarious". A member of this race was Lieutenant Thralen, a crewman aboard the USS Enterprise.
Most Theskians on Theskia and their colony worlds believed in the Great Mother, and many saw her as a manifestation of the generative force in the universe. However there were those of the Old Faith who stayed secluded on the homeworld, believing the galaxy was outer darkness and those who ventured out were heathens. Those of the faith who did not believe that the Great Mother literally birthed the world and tried to examine the universe were cast out of their family, or Ancient Den.
A common belief was that at the moment of death, the soul leaves the body and cannot return. If an individual were resuscitated, that individual would be an outcast, as a body without a soul. Knowledge of this was required in the Social Anthropology course at Starfleet Academy. (TNG novel: Metamorphosis)