DS9 centers on the formerly Cardassian space station, Terok Nor. After the Bajorans liberated themselves from the long, brutal Cardassian Occupation, the United Federation of Planets is invited by the Bajoran Provisional Government to take joint control of the station, which (originally) orbits Bajor. The station is renamed Deep Space Nine.

    * Benjamin Sisko (Avery Brooks), the Human Starfleet officer placed in charge of Deep Space Nine. At the start of the series, he is a grieving widower (his wife having been killed by the Borg at the Battle of Wolf 359) and the father of a teenage son. He and Jadzia Dax discover the Bajoran wormhole, which the Bajorans believe is the home of the Prophets, their gods and protectors. The Bajorans hail Sisko as the Emissary of the Prophets, an exalted religious status that initially makes him very uncomfortable. Due to his exemplary leadership, at the end of the third season, he is promoted from commander to captain.

    * Kira Nerys (Nana Visitor), a Bajoran militia major (later promoted to colonel), former guerrilla fighter during the Cardassian Occupation, and Sisko's second in command. She is initially suspicious of the Federation's intentions toward her planet, but grows to trust and befriend the rest of the crew. Like most Bajorans, she is deeply religious, which makes it awkward having the Emissary as her commander. Ro Laren, a character from Star Trek: The Next Generation, was the first choice of the producers for Sisko's first officer, but Michelle Forbes did not want to commit to a television show.[2]

    * Odo (Rene Auberjonois), the station's incorruptible chief of security. He is a Changeling, capable of assuming any shape he wishes. He was found and raised by the Bajorans. Odo yearns to find his own people, but when he finally does, he is less than pleased to discover that they rule the Gamma Quadrant with an iron fist.

    * Julian Bashir (Alexander Siddig), the chief medical officer. Although Human, his parents had him illegally genetically enhanced when he was a child because he could not keep up with his peers. Somewhat tactless, he nevertheless develops friendships with several of the station's residents, particularly Miles O'Brien and, more ambiguously, a mysterious Cardassian named Garak. Siddig appears in the opening credits by a shortened form of his birth name, Siddig el Fadil, for the first three seasons. He appeared as Alexander Siddig after he married co-star Nana Visitor, which placed their names together in the alphabetical cast credits, although his stated reason for the name change was that he discovered that viewers did not know how to pronounce his name.[3] Siddig continued to be credited as Siddig el Fadil when he directed.

    * Jadzia Dax (Terry Farrell, seasons 1-6), the Trill science officer. She shares her life and thoughts with a long-lived symbiont named Dax, which has already experienced seven prior lives "Joined" with other Trills. The previous host, larger-than-life rogue Curzon Dax, had been a close friend of and mentor to Sisko.

    * Quark (Armin Shimerman), a Ferengi bar owner. Like most of his species (with the notable exception of his brother Rom), he is extremely greedy and willing to do whatever it takes to acquire more latinum. This almost invariably brings him into conflict with Odo.

    * Miles O'Brien (Colm Meaney), the Human chief of operations. He keeps the station in working order. He is married to botanist Keiko, and has a daughter, Molly, and later a son, Kirayoshi. O'Brien is the first non-commissioned main Starfleet character, reprising a supporting role from many episodes of Star Trek: The Next Generation.

    * Jake Sisko (Cirroc Lofton), Benjamin's son. He decides not to follow in his father's footsteps, desiring to be a writer and reporter instead.

    * Worf (Michael Dorn, seasons 4-7) DS9's fourth season added Michael Dorn as the Klingon Worf, who had recently finished seven years on Star Trek: The Next Generation, in order to boost ratings.[4] Worf transfers to DS9 when the brief war between the Federation and the Klingon Empire breaks out, and stays on as Strategic Operations officer and later as a liaison to the Klingon Empire. Worf eventually marries Jadzia Dax.

    * Ezri Dax (Nicole de Boer, season 7) Ezri Dax was added to the show after the abrupt departure of Terry Farrell. Feeling that the large cast limited her screen time, Farrell did not renew her contract at the end of the sixth season and took a lead role on the sitcom Becker. The character was killed off and the writers introduced Ezri Dax (Nicole de Boer) as a young Trill who receives the Dax symbiont after Jadzia. Unprepared and untrained to be a host for the symbiont, she is often frustrated by aspects of the symbiotic relationship and the seven lifetimes worth of memories she inherits.[5]