Curzon Dax is a fictional character in the Star Trek universe. On the television show Star Trek: Deep Space Nine he was played by Frank Owen Smith and by Rene Auberjonois.

Curzon Dax was a joined Trill, from 2285 to 2367, the seventh host of the Dax symbiont. In his work as a Federation ambassador, he became friends with, and mentor to a young Benjamin Sisko, who affectionately called him "old man".

Dax was instrumental in the Khitomer accords which led to the Klingon Empire entering into alliance with the Federation. After this, Curzon became revered and respected amongst the Klingon people. One of his friends, a Klingon named Kang named his firstborn "Dax" and asked Curzon to be the child's godfather. When the young Dax was murdered by an alien known as "The Albino", Curzon joined Kang, Kor and Koloth (whose firstborn sons had also been murdered) in swearing a blood oath of revenge, which later was fulfilled by Jadzia Dax, the next host of the Dax symbiont.

When a young trill woman named Jadzia applied to the Symbiosis Commission to be joined, Curzon was her field docent. He fell in love with her and to cover up his feelings he recommended that she be dropped from the programme. Jadzia later re-applied and was the first candidate ever to be re-accepted, on Curzon's recommendation as he felt guilty.

Curzon died of "Jah-ma haron" on Risa, suffering a heart attack whilst in the company of a beautiful young woman. Upon his death, the Dax symbiont was transferred into Jadzia.

For Jadzia's zhian'tara, Curzon was temporarily embodied into Odo. Curzon took advantage of Odo's shapeshifting abilities to transform his new appearance closer to his own original appearance. Curzon and Odo wished to remain that way, and it was at this time that he finally admitted to Jadzia that he had fallen in love with her. Eventually Jadzia was able to convince Curzon to return to her so that they could be together always.