Kira was a last-minute addition to the cast. The original plan was to include the Raumschiff Enterprise: Das nächste Jahrhundert (1987) character of Ro Laren, but Michelle Forbes didn't want to do a series at the time.
When Colm Meaney was fitted for his Deep Space Nine uniform, he made two requests of the costume designers. He explained that unlike the officers, the non-commissioned Chief O'Brien was a working man. So he needed to be able to roll up his sleeves, and he needed pockets for his tools. The costume department altered his uniform accordingly.
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 Raumschiff Enterprise: Das nächste Jahrhundert (1987). Shimerman played the Ferengi officer Letek in The Last Outpost (1987) while Alaimo played the Cardassian officer Gul Macet in The Wounded (1991).
Colm Meaney was initially reluctant about signing onto the series. Meaney was comfortable playing O'Brien on an episode by episode basis for Raumschiff Enterprise: Das nächste Jahrhundert (1987), and at the time, was unsure if he wanted to play a full time television role.
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.