Curzon Dax led a very long and full life, having lived past his 100th birthday. (DS9: "Rejoined") According to Jadzia, Curzon was known to fall in love with someone new every week and he was romantically involved with members of several species, such as with Tavana's mother, Enina Tandro, as well as Arandis. (DS9: "Dax", "Meridian", "Let He Who Is Without Sin...", "Soldiers of the Empire") Curzon also loved to play tongo and enjoyed Juro Counterpunch as well as attending the Rujian Steeplechase. Like most of the other hosts of Dax, however, he had no musical talent. (DS9: "A Man Alone", "Equilibrium", "Meridian")
He was a top ambassador of the Federation in the late 2280s and the 2290s. In 2289, he represented the Federation during negotiations at the Korvat colony (early negotiations between the Klingons and the Federation), and in 2293, he represented the Federation at the Khitomer Conference.
The Klingon representatives at the Korvat negotiations were Kang, Kor, and Koloth. Curzon walked out of the conference while Kang was speaking, but this opened the door for Curzon to form a close relationship with all three Klingon warriors. Curzon and Kang became such good friends, that when Kang's first child was born, it was named Dax in his honor and Curzon also became his godfather. When the Albino killed the sons of all three Klingons, Curzon entered into a blood oath with them to avenge the deaths. (DS9: "Blood Oath") Sometime in his life, Curzon, during his zhian'tara, got Tobin Dax drunk. (DS9: "Facets")
Around 2339, Curzon was involved in resolving the Klaestron Civil War. He became a friend of the Klaestron General Ardelon Tandro and had an affair with Ardelon's wife Enina. In 2369, Curzon Dax was accused posthumously of treason and murder for killing Ardelon Tandro. The Dax symbiont was placed on trial for the crimes. When Ardelon's widow came forward to admit the truth, Curzon was cleared, and Jadzia Dax was set free. (DS9: "Dax")
Curzon met Benjamin Sisko in 2355 at Pelios Station when Sisko was an ensign. Curzon became a friend and mentor to him for over ten years. Sisko affectionately dubbed him "Old Man" and continued to use the name for both Jadzia and later Ezri. The two later served on the USS Livingston together. (DS9: "Emissary", "Dax", "Invasive Procedures")
Curzon had to deal with Sisko's temper at times. One time, Sisko was in an argument with an Argosian lieutenant, during which a drink was thrown in his face. Sisko intended to finish the fight, but Curzon held him back, eventually punching him in the jaw just to restrain him. He wore a ring which left a scar he held for many years later. (DS9: "Dax")
In 2369 Jadzia told Kira Nerys how they were once cornered by a party of hostile Kaleans on Rochani III. DS9: "Dramatis Personae") Sisko told Julian Bashir about Curzon's perverse pleasure giving Sisko assignments like the service for VIP guests. Sisko "graduated" from these assignments after he hit one of the guests for trying to seduce an unwilling female ensign. (DS9: "The Forsaken")
Curzon was also known and feared for "breaking" Trill initiates as a field docent for the Symbiosis Commission, and even eliminated Jadzia from the program. She later re-applied and succeeded in being approved for joining. She asked to be next in line for the Dax symbiont, and Curzon gave his consent. He later revealed to Jadzia during her zhian'tara that he had actually been in love with her. This, not any fault of hers, was the reason he originally eliminated her from the program, as he would have been unable to be around her as a supervisor. He was deeply relieved when she reapplied and accepted her re-application partly out of guilt that he had nearly cheated her of something she had wanted all her life. (DS9: "Playing God", "Facets")
Curzon once told Benjamin Sisko that the only persons who can handle Klingons were Klingons. In 2372 Sisko remembered this, and subsequently invited Worf aboard the station to investigate General Martok's task force. (DS9: "The Way of the Warrior")
Curzon died of strain incurred while seeking jamaharon on Risa with Arandis in 2367. His final days were spent in a hospital room yelling at the doctors and friends who were trying to keep him alive. He finally died as his family assembled at his bedside, as the symbiont was removed and implanted in a new host, becoming Jadzia Dax. (DS9: "Emissary", "Let He Who Is Without Sin...", "Blood Oath")
During Jadzia's zhian'tara, the Changeling Odo claimed the personality and memories of Curzon. During this time, Odo's shapeshifting abilities caused him to even look like Curzon – indeed, the Guardian speculated that Odo's shapeshifting abilities essentially allowed him to "join" with Curzon much like a symbiont would with a host – and Curzon was able to reunite with Benjamin Sisko. At first, Curzon and Odo wished to remain as they were, robbing Jadzia of Curzon's memories. But after talking with Jadzia (who needed a pep-talk first from Benjamin), Curzon admitted his love for Jadzia, acknowledged he was being selfish, and returned to Dax. Jadzia assured him that they would always be together through Dax. Curzon's restored memories also provided Jadzia with a first-hand idea of the joy and freedom Odo found in his shapeshifting abilities, while giving Odo a unique insight into life as a solid, prompting him to admit that food, drink, and other physical pleasures were so compelling he was amazed that Curzon had ever managed to get any work done. (DS9: "Facets")
|The hosts of Dax|
|Lela • Tobin • Emony • Audrid • Torias • Joran • Curzon • Jadzia • Ezri|
Verad • Yedrin
In "Emissary", Curzon was portrayed by Frank Owen Smith, who did not have any lines in the episode, and by Rene Auberjonois during Jadzia's zhian'tara in "Facets". The latter performer thoroughly enjoyed the opportunity which portraying Curzon gave him to depart from his usual performances as Odo. Shortly after DS9 Season 4 began, Auberjonois speculated, "I think Curzon may return at some point in the future." (Starlog, issue #222, pp. 29 & 30)
According to the script for "Afterimage", his name was pronounced as "KIHR-zahn". 
Curzon has appeared in many novels, including The Art of the Impossible (which showed him to have been a student of Sarek) and Forged in Fire, which reveals the origin of his blood oath to slay the Albino, as well as a meeting with Hikaru Sulu during Sulu's first mission as captain of the USS Excelsior.
His mirror universe counterpart (β) appeared in the novels The Sorrows of Empire and Rise Like Lions. The former depicts him as being appointed by Spock to be the Empire's Ambassador to the Klingon Empire until he is recalled and sent into hiding before the Alliance can conquer the Empire. The latter depicts him as still being alive in 2377, by which time he is the last surviving joined Trill in the mirror universe, although he subsequently passes Dax on to Ezri Tigan.
In the novel Forged in Fire, Curzon's pre-joining name is revealed to be Curzon Antrani.