Jadzia Dax is one of the Trill joined species, consisting of the humanoid host Jadzia, and the symbiont Dax. Jadzia is an expert in exobiology and astrophysics. She is also an excellent pilot. She enjoys Klingon martial arts, Klingon culture, collecting music, and the game tongo. Her father's name is Kela. Jadzia has one sister. She is the only person in her family who is joined with a symbiont. Jadzia did very well in the initiate program, however Curzon Dax recommended that she be dropped. She later re-applied and became the only person to do so. Jadzia was joined with the 350-year-old Dax symbiont in 2367 when Curzon died. Curzon requested the symbiont be joined with Jadzia because he felt guilty for having her dropped unjustly.

The Dax symbiont has had eight hosts: the eighth is Jadzia, the seventh host was Curzon, the sixth Joran, the fifth Torias, the fourth Audrid, the third Emony, second Tobin, first Lela. The Dax symbiont has been married five times: three as a bride, two as a groom, and has had nine children: five as a mother, and four as father. Curzon Dax was a Federation Ambassador to the Klingon Empire and helped negotiate the Khitomer Accords. Emony was an olympic gymnast. Torias was killed in a shuttle accident. Curzon befriended a young Starfleet Ensign, Benjamin Sisko.

In 2369, Dax was reunited with Sisko, when Jadzia Dax was assigned to Station Deep Space Nine, commanded by Commander Benjamin Sisko. Dax and Sisko discovered the Bajoran wormhole in the Denorius belt. In 2370, Verad forcibly removed the Dax symbiont from Jadzia and joined with it. The symbiont was returned in time for rejoining with Jadzia host. In 2371, Jadzia became ill and her body began to reject the symbiont. It was discovered that she had another host, Joran Dax, who was a murderer. The Symbiosis Commission tried to hide the memories from Jadzia. In late 2371, Jadzia participated in the zhian'tara, the Trill rite of closure, where she "meets" her previous hosts through the bodies of her friends. She was Lt. Cmdr. Worf's par'machkai and the two were married in 2374.

In 2374, Jadzia was killed by Cardassian Gul Dukat, who was possesed by a pah-wraith at the time. Dr. Bashir was unable to save the host Jadzia, but did manage to save the Dax Symbiont. The Dax symbiont was returned to Trill for re-joining.

Starfleet History
2359-2363 Attended Starfleet Academy
Degrees in Exobiology, Zoology, Astrophysics and Exoarchaeology.
2369 Assigned as Science Officer to Deep Space 9, Lieutenant.
2369 Commander Sisko and Dax discover the Bajoran Wormhole in the Denorios Belt.
2371 Accidentally transported back to the 2024 Bell Riots. Helped to restore the timeline.
2372 Promoted to Lieutenant Commander.
2374 Served on U.S.S. Defiant NX-74205 during Federation/Klingon Task Force against the Dominion.
2374 Participated in a successful covert mission to destroy a Cardassian/Dominion ketracel-white depot.
2374 Commanded U.S.S. Defiant in a successful covert mission to destroy a Cardassian/Dominion sensor array.
2374 Killed in the line of duty on Deep Space Nine by Dukat.

Jadzia Dax was first seen in "Emissary" (DS9).