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When the Nielsen ratings started to go down during the broadcasting of the third season, the studio pressed for radical ideas for the fourth season to increase the show's popularity again. Some of their suggestions included blowing up planet Bajor, or taking the action away from the station. They finally decided that the show needed a popular character from an earlier Star Trek series. Initially, the producers weren't too pleased, because they had set up a subplot within the Dominion War storyline where the Federation would be facing off against the Klingons, and were already having difficulties making it work. However, the studio decision turned out to be a blessing in disguise when someone suggested to introduce The Next Generation's Worf (Michael Dorn) to the cast as an intermediate between the Federation and the Klingons, which conveniently solved most of the script problems.
Kira was a last-minute addition to the cast. The original plan was to include the Star Trek: The Next Generation (1987) character of Ro Laren, but Michelle Forbes didn't want to do a series at the time.
Although we only rarely see it, there is an ATM in Quark's bar. It dispenses the various types of currency used by major races visiting the station: Federation credits, Bajoran litas, Cardassian leks, and Ferengi latinum.
Colm Meaney was initially reluctant about signing onto the series. Meaney was comfortable playing O'Brien on an episode by episode basis for Star Trek: The Next Generation (1987), and at the time, was unsure if he wanted to play a full time television role.
Armin Shimerman (Quark) and Marc Alaimo (Gul Dukat the Cardassian) appeared as one of the first actors to portray members of their respective species, and both appeared on Star Trek: The Next Generation (1987). Shimerman played the Ferengi officer Letek in The Last Outpost (1987) while Alaimo played the Cardassian officer Gul Macet in The Wounded (1991).
Michael Dorn did not want to reprise his role as Worf, since the daily make-up application was exhausting, and he was relieved to be able to move on. Dorn said that the salary he was offered made him reconsider.