A Starfleet officer from the Trill race, Jadzia was the latest host of a symbiont known as Dax who bonded with her, granting her memories of all its past life experiences to form a merged being. With several lifetimes under their belt, Jadzia had lived male and female lives and, according to Farrell while appearing at Star Trek Las Vegas this past weekend, had a pansexual orientation.
While Jadzia herself was 28 years old at the start of the series, the Dax symbiont was approximately 300 years old and open to relationships, regardless of the gender of prospective romantic partners, and was part of one of television's first same-sex kisses in the episode "Rejoined." Later in the series, Jadzia would enter a romantic relationship with Worf, reassigned from the Enterprise to join the crew of Federation space station Deep Space Nine, and marry him. However, tragedy would strike when a pregnant Jadzia was killed by Cardassian villain Gul Dukat in the Season 6 finale.
The Dax symbiont, with Jadzia's experiences and memories, would survive and be implanted in a new Trill host named Ezri, forming Ezri Dax. This new incarnation of Dax would attempt to enter a romantic relationship with Worf based on her predecessor's lingering feelings before entering into a committed relationship with Doctor Julian Bashir.