Malevolent beings once cast out of the Bajoran wormhole by the Prophets, who seek to destroy their rivals and take Bajor for themselves.
The Pah-wraiths are noncorporeal beings closely related to the Prophets who once lived in the Celestial Temple, the Bajoran wormhole. According to Bajoran faith they were expelled after a great conflict and imprisoned in the Fire Caves of Bajor, where their followers later sought them out.
They are destructive and deceitful, working through possession of living hosts. In The Assignment one took over Keiko O'Brien and forced Miles O'Brien to reconfigure the station to harm the wormhole. In The Reckoning a Pah-wraith inhabited Jake Sisko and fought a Prophet within Kira Nerys. Gul Dukat became their disciple, and in Tears of the Prophets he released one into an artifact, killing Jadzia Dax and closing the wormhole for a time.
In What You Leave Behind, Dukat and Kai Winn Adami tried to free the Pah-wraiths in the Fire Caves. Winn turned against Dukat at the end, and Benjamin Sisko threw himself and Dukat into the flames, sealing the Pah-wraiths away again and fulfilling his role as the Emissary.