Curzon Dax was a hero introduced in the Star Trek: Deep Space Nine pilot Emissary.
He was portrayed briefly by Frank Owen Smith on the DS9 pilot episode.
Born in the 2260s Curzon was known as Curzon Antrani until his joining with the Dax symbiont in 2285. As far as Curzon knew he was taking on the Dax symbiont after the previous host Torias had been in a coma for six months and the symbiont had to be removed after it was obvious that Torias was dying. What actually happened was that Torias had been dead for the past six months, and Dax had been joined to Joran Belar. The joining resulted in Joran Dax becoming unstable, and Joran was killed after he murdered several people. Dax was then joined with Curzon, but a memory block was put in place to keep Dax from remembering the joining with Joran. Curzon would go the rest of his life not knowing about Joran Dax due to the memory block, but occasionally he would not be 100% sure about the number of hosts before him due to that memory block briefly slipping.
Soon after the joining Curzon Dax become Trill's representative to the United Federation of Planets, and a student of Ambassador Sarek. He also became close to Federation President Hiram Roth, and at his request attended talks with the Kligon Empire's representatives at the Korvat Colony. Curzon walked out right in the middle of a speech Kang was making, and earned the respect of Kang, Kor, and Koloth for the way he conducted himself when Kang confronted him. Captain Hikaru Sulu of the Excelsior was less than impressed with what Curzon did, considering him a loose cannon. Curzon and Sulu would eventually become friends, and Curzon told him about his joined nature - which was something not widely known at the time.
Curzon helped Kang, Kor, and Koloth track down the Albino after the Albino bombed the conference at the Korvat colony. Even though they were unsuccessful in bringing the Klingon pirate to justice, they dealt most of his operations a major setback and helped mitigate a bioweapons attack on Qo'noS.
Following the explosion of Praxis Curzon was heavily involved in the peace process between the Empire and the Federation, helping to negotiate the treaty between the two former enemies. He earned the respect of many prominent Klingons, including Gorkon, Azetbur, Kang, Kor, and Koloth.
Over the next 80 years Curzon played a major role in the Federation's diplomatic efforts. He would continue to call Sarek when faced with a diplomatic issue that he needed help on. Flamboyant in his personality, Curzon was well known for his romantic conquests as much as his diplomatic conquests.
Curzon also served on the Trill Symbiosis Commission (TSC). During his work on the TSC he encountered a young woman named Jadzia Idaris, who he would recommend be dropped from the program after he found he couldn't deal with his feelings towards her. Jadzia did not take the rejection sitting down, reentering the program from the beginning and becoming the first initiate to graduate after having been dropped from the program previously.
In 2253 Curzon was assigned a young Starfleet officer named Benjamin Sisko as an attache. The two men would form a close mentor/student relationship, and Curzon would later describe Sisko as the best friend he ever had. By the 2360s, at over 100 standard years old, Curzon's health began to fail as his years of hard and fast living caught up with him. Learning that Curzon was dying Jadzia Idaris requested to be the next host for Dax when the time came, and Curzon did not object.
In 2367 while on Risa Curzon's health took a turn for the worst, and it was decided it was time for the Dax symbiont to move on to the next host. Dax was transferred to Jadzia Idaris not long afterwards, becoming Jadzia Dax in the process. All of Curzon's memories would live on inside Jadzia, and then in Ezri following Jadzia's death in 2374.