The Botha were a reclusive, apparently humanoid species who inhabited a region of space in the Delta Quadrant. As the Botha were hostile to outsiders, most starships which entered their space were never seen again.
In 2372, the USS Voyager entered their space and attempted to negotiate passage. Almost the entire crew was neutralized in an elaborate series of hallucinations, apparently caused by a powerful psionic field generated by three Bothan ships. The hallucinations began with various elements from the target's memory, and gradually became more inclusive until the person entered a comatose state, trapped in a fantasy reality.
The Bothan telepathy was defeated by Kes, whose telepathic abilities allowed her to "mirror" their attacks back onto the perpetrator (Although she required aid from The Doctor- whose holographic nature also rendered him immune- to focus long enough to do so). This immunity allowed her to trigger a resonance burst from the warp core, which blocked the Bothan's psionic field. However, both the Bothan on Voyager and his ships were illusions, disappearing after informing Captain Kathryn Janeway that he had no reason for attacking them other than that he could. The Botha's true nature was never discovered. (VOY: "Persistence of Vision")