Male Trill who was the seventh host to the Dax symbiont, a noted Federation dignitary, aficionado of Klingon culture, and something of a womanizer (which ultimately killed him). Joined from 2285 to 2367 — 82 years — Curzon was one of Dax's most enduring and distinguished hosts, and one of the most colorful. He was a close friend and mentor to Benjamin Sisko, who called him "old man," a habit that Sisko continued when Dax became Jadzia and then Ezri.

One of the highlights of Curzon Dax's illustrious career as a diplomat for the Federation was helping to negotiate the Khitomer Accords in 2293. But the road to that achievement was rocky. In 2289, four years prior, Dax walked out on a speech by Kang at the Korvat colony, angering Kang, but opening the door for understanding. Dax eventually won the respect of his Klingon colleagues and was deeply honored when Kang named his firstborn son for Dax, and made Dax the child's godfather. When the boy was murdered by the Albino, Dax swore a blood oath to avenge the death. Although Curzon Dax did not live to fulfill the promise, the eighth host, Jadzia, did so in 2370.

Dax also served as a Federation mediator on Klaestron IV during that planet's civil war in the 2330's. He became friends with General Ardelon Tandro and his family while stationed on the planet. Unknown to Tandro, Dax was also engaged in a love affair with Tandro's wife, Enina. Thirty years later, when Jadzia Dax was accused of Tandro's murder, Enina testified that at the time of her husband's death, Curzon Dax was in her bed.

Curzon first met Ben Sisko at the Palios Station when Sisko was an ensign, and they served together aboard the U.S.S. Livingston. They stayed good friends for nearly two decades. Curzon used to assign Ben Sisko to guide VIP guests while under his command so the Trill wouldn't have to deal with them.

Curzon acted as Jadzia's field docent and recommended she be dropped from the initiate program, noting that he felt she lacked a sense of purpose. She did not realize until years later that Curzon's harsh evaluation had spurred her to re-examine her purpose so that she eventually did win the opportunity for joining. Despite his early opinion of Jadzia, Curzon did not object when, at the end of Curzon's life, Jadzia asked to become the next host of the Dax symbiont. In 2371, Jadzia learned that the true reason for Curzon's recommendation was that he had fallen in love with Jadzia during the young woman's initiate program. Unable to deal with these inappropriate feelings, and unwilling to admit them to Jadzia, Curzon recommended that she be dropped from the program. Curzon would later admit to feeling so guilty about his actions that he nearly retired from the Trill Symbiosis Commission. Four years after Curzon's death, Curzon's personality reluctantly admitted his feelings toward Jadzia through her zhian'tara ceremony.

Curzon was not known to be punctual — he was even late for his 100th birthday party. Curzon had learned to play tongo and was fond of the game, a fondness that Jadzia retained. He was once thrown out of the infamous Barros Inn for setting the place on fire.

Curzon Dax, who never married, died in 2367. At the time of his death, he had been on planet Risa, making love with a beautiful woman named Arandis, who termed the experience "death by jamaharon." The Dax symbiont was subsequently implanted into Jadzia Dax.