The Trill who is joined to the Dax symbiont after Jadzia.
Ezri Dax is the Trill who becomes the ninth host of the Dax symbiont in the final season of Star Trek: Deep Space Nine, played by Nicole de Boer. Formerly Ezri Tigan, she was an ensign training as an assistant counselor aboard the USS Destiny, with no expectation of ever being joined, when the symbiont needed an emergency host after Jadzia's death.
The sudden joining leaves her overwhelmed by the memories of Dax's earlier hosts. She comes to Deep Space Nine, where Sisko helps her find her footing and she becomes the station's counselor. Her friends must adjust to a Dax who is a different person, and her dealings with Worf are awkward at first.
She is promoted to lieutenant junior grade during the season, and by the end of the series she and Julian Bashir begin a romance. Ezri is remembered for her journey from an unprepared newcomer to a confident officer.