- "They invaded the dreams of the prophet Theras and his followers, taking whatever forms they found there, whatever they would believe, and instructing them to keep anything larger than about the size of a B-wing from taking off."
- ―Luke Skywalker, on the Tsils
Theras was a male prophet who served as the original leader of the Theran Listeners, a Force-based organization that operated on the planet Nam Chorios. One night, while Theras was sleeping, the Tsils, a species of sentient crystals that lived on Nam Chorios, entered Theras' dreams and influenced him into believing that contact between Nam Chorios and the wider galaxy should not be permitted. Afterward, Theras ordered that no starship of a large-enough size to be fitted with heavy shielding should be allowed to land on Nam Chorios.
- Planet of Twilight (First mentioned)