Pah-wraith

In the fictional Star Trek universe, Pah Wraiths (also spelled Pagh Wraiths, Bajoran for Soul Wraiths) are the opposing force to the Bajoran Prophets. Non-corporeal life-forms, they were expelled from the Bajoran wormhole and imprisoned in the Bajoran Fire Caves on the planet Bajor. They serve as villains of the DS9 series, being served by one of the show's central villains Gul Dukat and threatening to destroy the galaxy in the show's final episodes.

They long for revenge against the Prophets who cast them out, even going so far as to possess the bodies of corporeal beings to further their goals. Keiko O'Brien, wife of Deep Space Nine's Chief of Operations Miles O'Brien, was used in a nearly successful attempt to kill the Prophets. (episode: "The Assignment")

In another incident, episode "The Reckoning", the Emissary (Benjamin Sisko) released a Pah Wraith and a Prophet from an ancient artifact. These beings fought on the Gates to the Celestial Temple (Deep Space Nine). In the fight, a Prophet possessed the (willing) body of Kira Nerys while the Pah Wraith possessed the (unwilling) body of Jake Sisko.

In "Tears of the Prophets", Gul Dukat unleashed a Pah Wraith from an ancient relic which possessed his body and proceeded to use an orb at Deep Space Nine to close the wormhole. Once this happened, the cult of the Pah Wraiths became more popular on Bajor. Once Sisko found the Orb of the Emissary (in "Shadows and Symbols"), the wormhole reopened and the Pah Wraith was again cast out.

In the final episode, "What You Leave Behind", Dukat and Winn Adami attempt to free the Pah Wraiths from their prison. Winn, who had abandoned her faith in the Prophets, returns to them and undergoes a change of heart, sacrificing her life in an attempt to stop Dukat. Eventually, Sisko and the Prophets return the Pah Wraiths - and Dukat - to the fire caves forever, never to threaten the galaxy again.