Current host of the Dax symbiont (as of series start), Jadzia has memories spanning several lifetimes. Dax's previous host, Curzon, was a friend and mentor...
After the (spoiler alert!) death of Jadzia, Ezri becomes the new host of the Dax symbiont and joins the crew as the station's counselor. Unprepared...
Former Prefect of Bajor during the Cardassian Occupation, Dukat is the station’s primary nemesis, and occasional ally.