Siddig El Fadil, later known as
Alexander Siddig was an early front runner for the part of series protagonist
Benjamin Sisko. Ultimately the producers thought he was too young for the role and instead offered him the part of Dr. Julian Amoros, who was subsequently renamed to
Julian Bashir;[6][7] the role of Sisko went to
Avery Brooks. Deep Space Nine was originally intended to have
Ro Laren, a character from The Next Generation as a main character. However, after actress
Michelle Forbes declined to sign on for a five- to six-year commitment for the series, the part was re-written to become Major
Kira Nerys, with
Nana Visitor cast in that role.[8] For similar reasons,
Famke Janssen turned down the role of
Jadzia Dax when offered, with
Terry Farrell becoming the last main cast member to be cast with filming already underway on "
Emissary".[9][10] Two actors who considered for main roles went on to be cast as recurring characters:
Andrew Robinson was beaten to the role of
Odo by
René Auberjonois, but was cast as the
Cardassian tailor/spy
Elim Garak;[11] similarly,
Max Grodénchik lost the role of
Quark to
Armin Shimerman, but was subsequently cast as that character's brother,
Rom.[12]
There were several actors who appeared in Deep Space Nine in roles they had previously played in other Star Trek series. The most prominent of these was
Colm Meaney, who played Chief
Miles O'Brien. Meaney had first appeared as an unnamed crewman in the pilot episode, "
Encounter at Farpoint", and went on to appear in a total of 52 episodes of The Next Generation.[13] Miles' wife
Keiko O'Brien had also appeared on The Next Generation and became a recurring character on Deep Space Nine, as played by
Rosalind Chao.
Majel Barrett appeared as
Lwaxana Troi, having also originally appeared in The Next Generation.[14] She was intended to be a recurring character in the new show,[15] and also continued to voice the
Starfleet computers as in the earlier series.[14]
The series had several long-running antagonists.
Marc Alaimo portrayed Gul
Dukat,[16] the
Cardassian former commander of Deep Space Nine who later led his people into joining the
Dominion. Dukat had been included in the series bible as a recurring character described as someone who "represents the continuing threat to our people".[17] There were several Dominion characters who appeared from the third season onwards, including
Salome Jens as the Female Shapeshifter,[18] and
Jeffrey Combs as Weyoun.[19] Combs was unique in Deep Space Nine for simultaneously playing two recurring characters – Weyoun and the Ferengi
Brunt – in the same episode, "
The Dogs of War".[20]
The fourth season saw a change in direction for the series with the producers asked to "shake up the show" by Paramount,[21] and the addition of a main cast member. Rick Berman suggested adding a
Klingon contingent to the show, adding
Michael Dorn to the main cast in the role of
Worf, which he had played for seven seasons on The Next Generation.[22] The changes also brought in
J. G. Hertzler as General
Martok, who became a recurring character.[23] Hertzler had previously appeared in the pilot of the series as a Vulcan Captain on board the USS Saratoga,[24] and Martok would end the series as the Klingon Chancellor.[25]
One further change to the main cast occurred between the sixth and seventh seasons. Terry Farrell elected not to renew her contract, so her character was killed in the final episode of season six.[26] She was replaced by
Nicole de Boer, who was cast as
Ezri Dax.[27]