Actor Allusion: Siddig was considered for the lead role because the producers mistakingly took his old age makeup for his real appearance. This is referenced in "Distant Voices" in which Bashir rapidly ages from a silver fox to a doddering geezer.
Actor-Shared Background: Like his character, Andrew Robinson is a claustrophobe. He had trouble wearing the prosthetics early on.
Aluminum Christmas Trees: "Far Beyond The Stars" seems to be a full episode about EC Comics's Judgment Day (printed around the same time this story is set), which killed the magazine when the publishers and editorial disagreed over having the hero be black.
Directed by Cast Member: Avery Brooks, Rene Auberjonois, Michael Dorn, Alexander Siddig and even guest stars Andrew Robinson and Jonathan Frakes get at least one shot behind the camera. And LeVar Burton, who appeared in The Next Generation, took a spin as well.
In fact, Burton was the fifth most prolific director on the series, while Brooks and Auberjonois share sixth place.
Follow the Leader: DS9 had trouble finding its feet initially, leaning on unresolved arcs from TNG and more or less sticking to its episodic format (not unlike VOY & ENT). As Babylon 5 began to makes waves with its much-hyped, five-year arc, the Dominion War was shortly introduced. The two would remain Dueling Shows for the remainder of their respective runs, with B5 wrapping up in 1998 (a year before DS9).
Iggy Pop as a Vorta in "The Magnificent Ferengi". Ira Behr lamented casting one of his idols (and a legendarily rowdy rocker) as such a monotone creature.
Played with in-Universe in the episode "Little Green Men", when Rom notices the similarities between historical activist Gabriel Bell and Capt. Benjamin Sisko. Fans, of course, know that the two are one and the same.
J.G. Hertzler, most well-known among Deep Space Nine fans for playing Martok, also played Sisko's commanding officer, the Vulcan captain of the U.S.S. Saratoga in the pilot episode "Emissary". He also later played changeling Laas in Season 7's "Chimera".
Which means he played Changelings twice, no? Several times in the guise of Martok, and once as Laas.
PRINCE HUMPERDINCK as Martus Mazur, Quark's one-episode commercial rival in the Season 2 episode "Rivals".
Now if only they could just have put Zek in that episode somehow. Surely they could have found a way.
Bill Mumy, best known as Lennier in rival show Babylon 5, or Will Robinson of Lost in Space, appears in "The Siege of AR-558". His one stipulation for crossing over was that he not have to wear any more prosthetics.
Mumy is the only B5 cast member to think that far ahead; both Andreas Katsulas (Tomalak on TNG) and Mary Kay Adams (Lady Grilka on DS9) were stuck with rubber foreheads.
Speaking of B5: Captain Kate Lockley guest-starred as a Cardassian engineer who butts heads with O'Brien. (She later tried bumping something else, but alas, he's happily married.)
Melora is Dr. Grace Holloway from the '90s Doctor WhoTV movie.
Melora (from the eponymous season 2 episode) was meant to be the permanent science officer, but was replaced with Dax and reused as a one-off guest character — thus cheating poor Bashir out of a romantic interest yet again.
Alexander Siddig originally tried out for the part of Sisko (!), but was turned down for being too young.
More understandably, Andrew Robinson tried out for the part of Odo.
Michelle Forbes, playing the part of Ensign Ro, was originally supposed to be Deep Space Nine's token Bajoran in the cast. Forbes didn't want to commit to a full television series, so the new character of Major Kira was created. Ro would end up serving as the station's chief of security in the relaunch novels, however.
Robert Hewitt Wolfe planned to end "Second Skin" on an "The End... Or Is It?" ending, with Bashir unable to determine whether Kira is actually a Cardassian. This left open the possibility that Kira was unknowingly a Cardassian agent all along, and that the Obsidian Order had been telling the truth.
When the Dominion invaded Federation space, Vulcan was pitched as one of the occupied planets. Ron Moore commented that Vulcan "carried too much weight," so Betazed was overthrown instead. Ironically, J.J. Abrams would happily blow Vulcan to smithereens in the 2009 movie.
The writers considered a Kira/Dukat Foe Yay scenario (season 4's "Indiscretion", introducing Dukat's half-Bajoran love child Ziyal, is artifact to where things may have headed). However, Nana Visitor (Kira) flatly refused to do anything of the sort, pointing out that he was guilty of the brutal occupation and near-genocide of Kira's species. Instead, the storyline was given to Kira's mother Meru as Dukat's "comfort woman" during the occupation in "Wrongs Darker Than Death Or Night." Similar to Michelle Forbes inadvertently causing the creation of Kira, this storyline probably worked out better for Kira's character.
While "Trials and Tribble-ations" is regarded as one of the best episodes of the series and a fitting 30th Anniversary for the franchise, there were numerous other ideas which were tossed around. One of which was having the Deep Space Nine crew visit the mobster planet from "A Piece of the Action", where they find that the inhabitants have gone on to emulate Starfleet as a commentary on Star Trek fandom.
The writers originally toyed with the idea of killing off Jadzia Dax in the Season 6 episode "Change of Heart" rather than in "Tears of the Prophets", the season finale. The idea was that Jadzia would manage to convince Worf to continue their mission without her and leave her behind, in which case she certainly would have died. Worf would then have had even more angst than he ended up with to work through in the final season, having lost his wife out of choosing his career over her. Terry Farrell (Jadzia) was on board with it, but they ended up not going through with the idea.