The Thoi'han were ancient sapient species that appears to have existed much earlier then the Protheans. Long ago, they waged war with Inusannon over colonization of planet Eingana. The remains of starships can be found Eingana and it's moon of Barraiya. Both races inadvertently transformed the garden world of Eingana into a toxic hellhole, filled with mutant creatures which tended to have biotic abilities, because of all the Element Zero that polluted the planet. The Thoi'han are currently extinct, though its unknown whether this was the result of the Inusannon, the Reapers or something else entirely.
- Mass Effect 2 (mentioned only)