Jadzia Dax was one of the main cast members of Star Trek: Deep Space Nine. Portrayed by Terry Farrell, she served as DS9's science officer for most of the series until her tragic death in the Season Six finale, "Tears of the Prophets".
Jadzia Dax is a Trill, a humanoid race that co-exists with a species of sentient symbiotic life-forms generally referred to as "symbionts". The name Dax belongs to the symbiont that dwells within Jadzia's body and imbues her with the memories and experiences of its previous hosts. The Dax symbiont has lived for over three centuries and has been joined to nine hosts in that time with Jadzia being the eighth.
Throughout the series, Jadzia has forged many friendships aboard Deep Space 9, most notably with her commanding officer Benjamin Sisko, who was familiar with Curzon, the seventh Dax host. She took much pride and joy in her work as a science officer and off-duty she enjoyed indulging in Klingon culture and playing the Ferengi game tongo with Quark. In the series' sixth season, she became married to Lt. Commander Worf and joined the House of Martok.
Jadzia was a strong, independent woman with a jovial and often flirtatious nature. She tried to take pleasure from everything she did in life and came to show a particular interest in the Klingon culture. Her personal interests were numerous and varied and included many of the talents and passions of her previous hosts, such as her sixth host's appreciation for music.
In the sixth season episode "Tears of the Prophets", Jadzia remained behind on Deep Space 9 when most of her crewmates took part in the Federation Alliance assault on the Chin'toka system. She had been taking hormonal treatments that would allow her and Worf to have a baby and had visited a Bajoran Temple on the promenade to give thanks to the Prophets for their blessing. Sadly, her prayer was interrupted by the malevolent Gul Dukat, who had been possessed by a demonic entity known as a Pah-Wraith. Intent on releasing the Pah-Wraith into the Bajoran Wormhole and destroying the power of the Orbs of the Prophets, Dukat wanted to reach the Orb of Contemplation but Jadzia stood in his way. Granted telekinetic powers by the evil spirit, Dukat struck Jadzia down, mortally wounding her. Jadzia would later die in the infirmary, though Dr. Bashir managed to save her symbiont which would later be planted into a new host.
Dax lives on
Although Jadzia died, the Dax symbiont was saved. It required a new host to survive and so it was taken aboard the USS Destiny which was to transport it to the Trill homeworld. In transit, however, the symbiont's condition deteriorated and needed a new host immediately. Ezri Tigan, an unjoined Trill and member of the Destiny crew, was the only Trill aboard and so the symbiont was planted within her. Trill joining normally requires years of study and preparation to determine if a Trill is fit to be a host or not, and since Ezri had not received any kind of preparation for joining, she initially found herself overwhelmed by all of the different memories and personality aspects carried by the Dax symbiont. She would eventually learn to cope with it, however, and she would transfer to Deep Space 9 and serve as the station's official Starfleet counselor.