Star Trek Canon Special Note
Not everything listed in the origin is Canon. That is because only television shows and movies are considered canon for Star Trek. This being a comic website there are many things here that are not canon. So unless it is contradicted in film it should be listed as part of the character biography.
Jadzia is a trill who carries with her a symbiont called Dax. When a trill and symbiont are joined it is customary to take the name of the symbiont as the last name. The Dax symbiont had seven hosts before Jadzia however she was only aware of six of them as won had been suppressed by the Guardians of the symbionts. The Dax symbionts in order were, Lela, Tobin, Emony, Audrid, Torias, Joran (the suppressed host) and Curzon.
There are a very small amount if symbiont compared to trills so there is a very difficult process to be accepted to be a trill. Jadzia washed out in her first attempt but was allowed to reenter and became the only Trill to be joined after once being washed out. One of the things Jadzia did to help her in her process to be joined was to join Starfleet and she became a well regarded Science Officer.
The idea for the character of Jadzia came form an episode of Star Trek: the Next Generation. The producers of a new show Star Trek: Deep Space Nine like the idea of the character from the episode and wanted to cast an attractive woman for the role. Terry Farrell was cast for the role but when the test shots were done for the program the producers decided she didn't look very good with the forehead prosthetic that the original character had so they changed the way the race looked by adding spots along the side of her body. They felt this gave her an attractive look for the show.
Terry Farell stayed with the show six of the seven seasons the show was on the air. The reason for her leaving was that she new the show was ending and wanted to get another role on a television show called Becker. The producers understanding the request let her leave and killed the Jadzia part of the character off and joined the Dax symbiont to another Trill called Ezri. Thus Ezri Dax joined the cast for the seventh season.
After Jadzia was joined she was stationed at the Deep Space Nine space station orbiting Bajor. Shortly after she arrived there she discovered the first stable wormhole reaching the Gamma quadrant and it was one of her proudest memories. The Bajoran people believed that she and her Commander Benjamin Sisko had discovered the the celestial Temple and that Sisko was the prophesied Emissary. Something Sisko tried to stay away from for a long time.
Dax and Jadzia were fast friends as Sisko had always looked up to Jadzia's previous host Curzon. Curzon Dax was a mentor to Ben and Ben would even call her "Old Man" almost as a way to be comfortable in the unusual situation of Jadzia now being a young and attractive woman. This relationship would come under a strain when Jadzia Dax is accused of the murder of a great leader of another planet. The prosecution claimed that the Symbiont was guilty and that it is only escaping justice by getting a new host. Benjamin was the defense and arguerd that Curzon Dax no longer existed and that Jadzia Dax was a new being. This all remained undecided in Bajoran law as the case was dismissed when the wife of the murdered man gave Dax the aliby of sharing her bed at the time of the murder.
Only a short time later the symbiont was literally stolen from body by a Trill named Verad Kalon. Verad became the ninth symbiont although no one still new about Joran at this point. Verad joined with Dax and became Verod Dax but only for a few hours and it was returned to Jadzia making her the eighth and ninth Host to be joined to Dax.
It was a year later the the Joran Symbiot was discovered by repressed memory by Jadzia. It was later a huge cover up as the a murderer stole the symbiont and he was joined proving that more people were able to join than than the population knew. This was a huge fear for many of the Trill people who know as they were afraid of riots or worse should the regular population ever found out. They would rather let Jadzia die from her condition rather than let her have the memories. Fortunately, for Jadzia, Sisko and Dr. Julian Bashir discovered the truth and threatened to reveal the secret unless Jadzia was helped. At this they relented and Jadzia was allowed to know her past life as Joran Dax.
Just like Dax's previous host Curzon Jadzia had a strong connection with the Klingon world and even had a Klingon Godson who as Curzon swore a blood oath to punish the Klingon that killed him. As Jadzia she honored that request and helped kill the man responsible although she did not strike the actual kill. Two of the four who went on the mission also died in the battle.
When Worf was stationed at Deep Space Nine the two quickly fell in love and were married after a couple of years. It was a very loving relationship and caused a problem when Worf abandoned an important mission to save her life. In doing so he got his second reprimand on his record. Unfortunately, fate was against the couple and Jadzia was killed a few months later by Dukot while she was in the temple thanking the profits for her pregnancy.
The death took the whole crew of Deep Space Nine hard. Worf went on to fight a battler in her name with friends like Martok, Bashir, Miles O'Brien and even Quark to get her into Sto-Va-Kor. The Dax symbiot however was saved and joined to ironically an unwilling host named Ezri Dax. This was due to her being the only one available and if she refused Dax would have died. Once joined however the host could not be separated from the host without the host dyind so Ezri Dax was created and she carried on the memories of Jadzia and even went back to Deep Space Nine as a councilor. This made things difficult especially for Worf but she found her place and even fell in love with Julien who had ironically always been in love with her even when Dax was a part of Jadzia.