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Jeffrey Combs has the distinction of portraying nine different characters on various Star Trek series. He played the roles of Brunt, Weyoun, Shran, Tiron, Agamus, Kevin Mulkahey, Penk, Krem, and a holosuite guest. He is one of only five actors to play seven or more different characters in the Star Trek franchise, the others being Randy Oglesby, J.G. Hertzler, Vaughn Armstrong, and Thomas Kopache. Coincidentally, Combs has appeared on Star Trek with all four of those actors.
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).
Constable Odo was originally envisioned as a young Clint Eastwood type. When Rene Auberjonois was called in for his audition, the casting director told him that none of the previous actors had been "grouchy enough". So Auberjonois improvised his lines using his most gravelly voice, and secured the role. Odo's scoff eventually became such a character trademark that the screenwriters would often script it into his lines (as "harrumph!"), much to Auberjonois' annoyance.