All of the main cast (with the exception of Cirroc Lofton) and their Mirror Universe counterparts.
Bashir gets reckd by Voyager's Robert Picardo (as Dr. Lewis Zimmerman and the Emergency Medical hologram) in "Dr. Bashir, I Presume". The "archaic" EMH is confronted by the even more presumptuous Holo-Bashir, triggering a four-way catfight between the holograms and their templates.
Jeffrey Combs, playing clones of the same character, gets to play a good and evil (ie. normal) version of Weyoun arguing over a commlink; he also played the Ferengi character Brunt. Combs always wanted to appear as both Weyoun and Brunt in a single scene, but never got the chance. He did, at least, get to play both characters in the same episode, Season Seven's "The Dogs of War". At one point, a scene change cleverly cuts directly from Brunt to Weyoun.
"Far Beyond the Stars", "Shadows and Symbols", and (to a lesser extent) "Badda-Bing, Badda-Bang" and "What You Leave Behind" showcased the cast sans fards. One interesting example is the episode "Far Beyond The Stars". The entire regular cast show up as humans in Sisko's vision of the 1950s on Earth. Cast members who usually appear in heavy alien makeup here appear almost unrecognizable without their prosthetic, leading to a weird "you look familiar..." deja vu feeling (which reflects Sisko's state of mind) until you match up the actors with the characters they usually play. Combs appears out of makeup twice: once as a corrupt detective in the Bennyverse, and again in "What You Leave Behind" as one of the creator cameos in Vic's lounge.
Acting in the Dark: Alexander Siddig only found out that his character was actually a Changeling impersonator for several episodes until the episode where it was revealed.
Like his character, Andrew Robinson is claustrophobic. He had trouble wearing the prosthetic early on. Garak also spoke of posing as a gardener while conducting surveillance on Romulus. His stint at the Cardassian Embassy coincided with a number of mysterious deaths that year, including a Romulan proconsul who was found poisoned. This is an in-joke by Andrew Robinson, who is passionate about gardening in real life but hasn't murdered anyone. (That we know of.)
When Kira is complaining about how she feels being pregnant with the O'Brian's baby she says "This is YOUR fault!" to Dr. Bashir. Nana Visitor was really pregnant with Alexander Siddig's child. Also, in the Bennyverse ("Far Beyond the Stars"), the pulp authors played by Visitor and Siddig are a couple, just like in real life.
Sisko has an extensive collection of African art (like Avery) which he gradually moves to his new space station digs. In "Past Tense" and "Badda-Bing, Badda-Bang" he's revealed to be something of a Civil Rights historian (again, like Avery), making him a perfect guide into the underbelly of Federation culture. Also, Avery is a little off-beat at times.
B-Team Sequel: The first Trek series to be created without direct input from Gene Roddenberry, and it shows, especially in the later seasons, which are much Darker and Edgier than Roddenberry's optimistic vision of humanity's future.
The producers were so impressed by Alexander Siddig's performance in A Dangerous Man: Lawrence After Arabia that they intended to offer him the role of Sisko, until they actually met him and realized he was far too young for the part (having been aged up for the film). Instead, they cast him in the role of the station's doctor, originally called Julian Amoros but renamed Julian Bashir to better suit Siddig's background.
William Sadler was considered for Sisko. He later went on to portray Section 31 operative Luther Sloan.
Tim Ransom (Jack the Augment) had previously auditioned for Bashir.
Hilary Shephard Turner (Lauren) also tried out for the role of Jadzia. This is referenced in "Chrysalis" when she turns up in a Starfleet sciences uniform. Alarmingly, she is a dead ringer for the dearly departed Trill!
Kurtwood Smith was offered the role of Odo, but turned it down, as he didn't want a role that required prosthetics Ironically, he would show up in an episode as Odo's Cardassian predecessor as chief of security on Terok Nor.
The Cast Showoff: Inverted in "Take Me Out to the Holosuite". Max Grodénchik was actually a successful semi-professional baseball player who seriously considered going pro before becoming an actor instead. The reason Rom plays left-handed in that episode despite not being left-handed in the rest of the show is that Max simply couldn't play badly enough to convincingly portray the worst player on the team any other way.
Terry Farrell's favorite episodes are "Far Beyond the Stars", "Fascination", "Playing God", "Blood Oath", "You Are Cordially Invited", and "Change of Heart".
Creator's Pest: Andrew Robinson didn't care much for Mirror Garak, finding him to be a boring one-note toady who lacked all of his Prime counterpart's nuance and menacing aura. The character's final appearance, where the Prime Universe Ferengis brag about how much more clever and competent their Garak is, followed by Mirror Garak being injected with his own virus and left for dead may have been a wink to the sentiment.
Even though Nog was supposed to be in his mid-teens at the start of the show, Aron Eisenberg was 24 years old when it premiered, and nine years older than Cirroc Lofton, who played Jake. Eisenberg had kidney problems since birth, which limited his growth. Lampshaded in the episode "The Visitor", where a flashforward some twenty years in the future featuring Nog and Jake has the latter transforming from Lofton into Tony Todd... while the former is still being played by Eisenberg.
Major Kira was supposed to be 26 at the start of the series, however Nana Visitor was 35 at the time.
Melanie Smith was 34 when she played 20-year-old Tora Ziyal in the show's fifth season. Oddly enough, this was downplayed by Ziyal's first two actresses, Cyia Batten and Tracy Middendorf, who were 22 and 25 years old respectively; however, the producers decided they were both too young for the Ship Tease they wanted to set up between Ziyal and Garak (Andrew Robinson was 55 at the time).
Development Gag: The name of the episode "The Siege of AR-558" comes from 558 being the development number of the episode. It fits the overall idea of the battleground being such a random nondescript place that it doesn't even have a real name.
Doing It for the Art: Frank Langella's uncredited appearance in the first three episodes of Season 2. He didn't want to make it seem like he was appearing on DS9 for money or exposure.
Dueling Shows: With Babylon 5 during its '94-'95 run. B5 auteur J. Michael Straczynski has claimed for years that Paramount stole his story treatment, but internal company memos have come to light hinting that the idea circulating around before he pitched his show. The two would remain rivals throughout their respective runs, with B5 wrapping up a year earlier in 1998. The two shows' similarities begin at being set on a space station at a trade crossroads and don't stop there:
At the beginning of the series, the human station commander is a traumatized veteran of a space battle near Earth, where humanity was almost defeated for good. He has an important destiny in the religious prophecies of one of the major alien races, which he initially doesn't understand but eventually comes to embrace.
The series takes place in the aftermath of formerly occupied planet regaining its independence from its imperialistic oppressors. The most prominent character from the imperialist race, seeking to recover his planet's former glory, allies his people with a powerful, sinister alien race from the other side of the galaxy, leading to an all-out war between the powerful aliens and the station's staff. The most prominent character from the formerly subjugated race plays a major role in helping the former imperialist race escape the powerful aliens' control.
The station's second-in-command is a tough woman with a take-no-prisoners attitude. The doctor is talented but arrogant and a bit of a playboy. At the beginning of the third season, a Cool Starship is introduced, enabling more episodes set away from the station. A main actress unexpectedly quits the show before the final season.
A (barely) oblique reference is made to this on B5. In one episode, a gift shop is set up on the station. One of the characters loudly derides this idea, saying "This isn't some deep-space franchise! This station is about something!" It should be noted that the writer of this episode, Peter David, has written several Star Trek novels. (When he wrote that line into the B5 script, it was with the expectation that JMS and friends would change it, if only to a more subtle jab, before shooting; upon learning that the line was filmed and broadcast verbatim, David remarked to JMS that "...you people are dangerous over there, aren't you?")
The Deep Space Nine writers weren't above including their own subtle jabs at B5. One episode featured Bashir having to chaperone a cadre of Ambassadors visiting the station and putting up with all the crap that comes with it. According to JMS, the writers of DS9 actually liked B5. The producers, not so much.
There are massive parallels between the Sheridan/Shadows and the Sisko/Pah-Wraith arc. Sisko is marked for death by the Prophets for defying them and takes a high-dive into the Fire Caves, 'killing' him while transferring his essence to a spiritual realm: the situation is a mirror of Sheridan's trip to Z'ha'dum and his later vanishing into the Rim.
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 make waves with its much-hyped, five-year war saga, the Dominion War was shortly introduced.
The intrusion of Section 31 into Federation politics is incredibly similar to B5's PsiCorp. J.J. Abrams revived Section 31 for the film reboot, making it Deep Space Nine's longest-lasting influence on Trek as a whole.
There was also an amusing incident involving actor Robert Foxworth, who had appeared on B5 as Earthforce General William Hague, part of the conspiracy to overthrow President Clark. He was then mistakenly double-booked by his agent as the very similar Admiral James Leyton on DS9's "Homefront"/"Paradise Lost " two-parter, resulting in Hague being killed offscreen in "Severed Dreams". (Bruce McGill said in an outtake for that episode that Hague couldn't be present because he was "doing Deep Space Nine.")
Enforced Method Acting: To have an episode where a character questions their entire sense of self is a big ask of any actress, but to claustrophobe Nana Visitor (who was used to a teeny prosthetic on the nose), it was like entering an iron maiden. In "Second Skin", she claws at her Cardassian face as though it is a mask that she wants to rip off and she actually did, pulling apart her latex and fleeing the set in terror. They somehow managed to get the episode in the can, but it was her hardest episode to film.
Executive Meddling: A good one. The idea of the Vorta being entirely a cloned species was the result of the producers being extremely impressed with Jeffrey Combs' performance of Weyoun and wanting to bring him back.
Andrew Robinson explicitly played Garak as bisexual in his first scene with Dr. Bashir. Writer Robert Hewitt-Wolfe corroborated this, adding that Bashir was supposed to be oblivious to his advances (though in more recent discussions on Alexander Siddig's Zoom club, Siddig and Ira Stephen Behr have suggested otherwise). This plot thread was swiftly bundled out of sight by Paramount, though it doesn't entirely go away (at least as far as Garak's mannerisms go.) In the documentary about the show, Behr has said that everyone knew Garak was "gay" but that they knew that it was a fight with Paramount that they wouldn't win.
Fake Brit: Actually averted with Julian Bashir, played by Alexander Siddig, an English Arab born in Sudan. This makes one of only three times in the franchise a non-American main cast member was played by an actor of the same nationality (the others being Colm Meaney as Miles O'Brien, and Dominic Keating as Malcolm Reed).
Fake Russian: Major Kira is reimagined as Colonel Anastasia Komananov ("Gay-Chee-Pee"), in Bashir's totally-not-James Bond holoprogram. Even Nana Visitor, an American, gleefully admitted that it's a terrible accent. This is commented on by Vic in "His Way". When pressed, he admitted that his sexy Kira duplicate, "Lola Chrystal", is just a modded version of the Colonel Komananov hologram and that it took him forever to get rid of her horrid accent.
Kai Opaka was called "Deep Space Nun" during the first season but was Put on a Bus midway through the season.
A number of fans refer to Jadzia as "Sex Giraffe" due to her giraffe-like spots and, well...
SF Debris coined the name "Ben Sisko's Mutha***in' Pimp Hand" for the Defiant, which appears to have caught on over the Internet.
SFDebris also coined "This is the one that even the Prophets call 'The Sisko'. First name: 'Don't F*** With'."
Damar was derisively referred to as "Dumbar" on certain fan forums for his blind loyalty to Dukat. Of course, this was before his HeelFace Turn.
Gay Panic: This was the initial reasoning behind the character of Ziyal - Garak was just a little too into Bashir for the executives' comfort (this was absolutely deliberate, by the way - Andrew Robinson, who played him, said he played Garak as omnisexual and very into Julian). He never got together with her, and seemed frankly baffled by her romantic feelings toward him, so the jury's out on how effective she was.
It's been said that Avery Brooks, Armin Shimerman, and Marc Alaimo took their roles very seriously (Brooks' temperament was partially due to Method Acting, Shimerman always fought against Ferengi as comic relief and Alaimo, despite technically being a guest star, would behave as though he was the lead). During the first few years with TNG filming next to them, when people were actually talking and laughing, the producers knew that Marina Sirtis had wandered over to visit some friends. Upon joining the cast in the fourth season, Michael Dorn said it took him some time to get everyone to lighten up.
Alexander Siddig claimed that Avery Brooks took to him early on in the series, noting that they were both POC on a sci-fi show. This bond did not last, when Brooks terminated their friendship mid-way through the run and was hostile to him from then on. Siddig claims to not know what he'd done.note The difference may have been ideological: Siddig is on record saying that Bashir just happening to be of North African descent and that being wholly incidental to his character was enough of a powerful statement for him in terms of racial progressivism (he also changed his stage name from the very Arabic "Siddig El Fadil" to the European "Alexander" partway through the show's run); Brooks, on the other hand, grew increasingly vocal about addressing Benjamin Sisko's African-American heritage in-story, from directing the acclaimed episode "Far Beyond the Stars" to adding in a line denouncing the inherent racism of 20th century Las Vegas and convincing the writers to change the show's ending as it looked like Sisko was abandoning his pregnant wife. Brooks allegedly was difficult to work with as a director as well as a cast member, and only a few of the regular cast would consider him a friend.
Many years later, in William Shatner's The Captains documentary, Brooks (alone among the captains - by contrast, Kate Mulgrew in particular has a very good rapport with Shatner) is unresponsive and evasive toward Shatner's line of questioning, frequently trying to change the subject by playing music. Shatner plays this off as Brooks being something of a Cloud Cuckoo Lander but it's clearly not good faith interview conduct.
Brooks declined to be interviewed altogether for the What We Left Behind documentary, the only major cast member to do so (though according to Ira Steven Behr he did have input behind the scenes). He has also made it clear that he has no intention to reprise his role despite Patrick Stewart, Kate Mulgrew, and Scott Bakula all agreeing to return to the franchise.
Baseball players in "Take Me Out to the Holosuite". Aside from Avery Brooks (Sisko) and Cirroc Lofton (Jake), the actors playing the Ferengi were the best baseball players in the cast. In fact Max Grodenchik (Rom) played college ball. The Ferengi being who they are, however, forced them to play left-handed and employ other tricks to look horrible on film.
Armin Shimerman has been on the board of directors of the Screen Actors Guild and worked against various entertainment corporations to secure actor's rights. Quark is a staunch anti-union and anti-worker's rights Ferengi. Then again, since Bioshock came out, he's given interviews stating his appreciation of Ayn Rand's books note Which is even more ironic, considering that the character Shimerman plays in BioShock, Andrew Ryan, and pretty much the entire rest of the game, is a slow, surgical dismantling of Rand's entire ideology, so he may not be so easy to pigeonhole.
Similarly, avowed socialist Wallace Shawn plays Grand Nagus Zek, leader of a race whose greatest value is acquiring profit.
McLeaned: Jadzia Dax was killed off after contract re-negotiations with Terry Farrell fell through (the early makeup calls were getting to be too much; several cast members had reached their wit's end by that point). Terry left the show in Season 6 to join the cast of Becker. She later regretted this decision, calling Jadzia a "superhero."
Money, Dear Boy: 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.
Quark's mother, Ishka was played by Andrea Martin in her first appearance, and Cecily Adams in all subsequent appearances. According to Armin Shimerman, Martin disliked acting in heavy makeup, and declined to reprise the part.
Tora Ziyal was played by Cyia Batten for her first two appearances, but the producers decided that she was too young for the part and replaced her with Tracy Middendorf for Ziyal's third appearance. Due to Middendorf proving allergic to the prosthetics and having poor chemistry with Garak's actor, Andrew Robinson, however, she was replaced by Melanie Smith for all of Ziyal's subsequent appearances.
Though apparently Klingons physically mature faster than most races... Alexander would have been about 8 years old when he began military service. Being 1/4 human didn't seem to matter any considering future Alexander seen on TNG looked fully Klingon regardless of minor human genetics.
It's mentioned in an episode of Voyager that in Klingon/human hybrids, Klingon DNA is dominant (hence why Miral Paris, who is only 1/4 Klingon, still has visible ridges on her forehead).
Production Posse: Ira Steven Behr was the executive producer and showrunner of both this series and The Twilight Zone (2002). Seven writers (Behr himself, Hans Beimler, Robert Hewitt Wolfe, Bradley Thompson, David Weddle, James Crocker and Frederick Rappaport) and four directors (Jonathan Frakes, Winrich Kolbe, Allan Kroeker and John T. Kretchmer) worked on both series.
Reality Subtext: Behind the scenes, Armin Shimmerman frequently campaigned for Quark and Ferengi in general to be treated with more respect by the show and not be used simply as comic relief. While the various characters get to kick Quark pretty much at will through the whole series, he occasionally gets the opportunity to stand up for the dignity of his species.
Near the end of DS9, Dr. Bashir asks Odo to donate part of his natural goo to help figure out how to grow new organs. Come the early 21st Century, and humans have nearly perfected the ability to grow organs in a lab - not, admittedly, organs that can change to become the one that is required by an impending surgical procedure (which is what Bashir was aiming for).
Bashir wanted it to help find a way to grow organs on the battlefield - it's on thing to grow a new organ for a lung transplant when someone has been ill for a couple of months, but it's hard to know how many lungs, hearts, etc to have on standby on a battlefield, nor do you often have the time to grow them as the patient could die before they are fully mature.
A joking reference by Odo to Admiral Ross as "Bill" in "Image in the Sand" was taken literally by the writing staff, resulting in his canonical first name. (As well as confusion for sharp-eyed viewers, as his office nameplate had previously established his first name to be Cliff!)
Morn was originally scripted and shot to speak a few lines early on in the series. However, when the episodes were edited down to fit the time slot, all of Morn's speaking scenes ended up on the cutting room floor. When the writers noticed the coincidence, they decided to turn Morn's silence into a Running Gag. Reportedly the guy who went through the effort of designing and building Morn's prosthetic makeup to include a moving mouth was not happy.
The entire concept of the Vorta being a clone race came about entirely because the crew regretted killing Weyoun off after seeing Jeffrey Combs' fantastic performance, and wanted some way to bring him back.
Troubled Production: This was probably the Star Trek series with the least problematic production history, though there were a few speedbumps in the seventh and final season:
The first was a result of Jadzia Dax actress Terry Farrell quitting the series after a dispute with executive producer Rick Berman, resulting in Jadzia getting a bridge dropped on her in the sixth season finale. She was replaced by Nicole de Boer, playing the new part of Ezri Dax; the producers tried to distinguish her from the extremely competent Action Girl Jadzia by making her more nervous and incompetent, but this backfired and resulted in a widely negative response to the character, forcing the later spin-off novels to retool Ezri to make her more like Jadzia had been.
The second major issue came when they ended up massively over-spending on the visual effects for the destruction of the USS Defiant in "The Changing Face of Evil", leaving them with only about two or three episodes' worth of effects budget for the final six episodes (bearing in mind that the finale was a two-parter). This limited them to largely using Stock Footage for effects shots in the rest of the season, and notably hurt the third-last story, "Extreme Measures," by forcing them to ditch the surreal dreamworld originally planned in favor of just re-using the regular DS9 and Defiant sets with no alteration.
The first six episodes of Season 6 were also a doozy. Designed as a very tight story arc involving the Dominion taking over the station and ultimately being expelled by the returning heroes, it quickly became clear that the crew were completely out of their depth in creating such an intensive long term story. The various episode crews were constantly over- or underestimating how much time and resources they would need, and eventually the B-plots of two episodes had to be completely switched so the first could be done on time, requiring some significant rewrites to keep the continuity making sense. Remarkably, this all turned out very well and the arc is generally regarded as one of the best parts of the show.
Vindicated by Reruns: The series polarized Star Trek fans when it aired, but years after it left TV if found a new audience on Netflix.
The behind-the-scenes mood was very dour. Avery Brooks, Armin Shimerman and Marc Alaimo took their roles very seriously: Brooks' temperament was partially due to Method Acting, Shimerman always fought against Ferengi as comic relief and Alaimo, though technically being a guest star, would behave as though he were a regular. Whenever people were actually talking and laughing, the producers knew that Marina Sirtis had wandered over from the nearby TNG set. Michael Dorn said it took him awhile to get everyone to lighten up after he crossed over.
If you study the behind-the-scenes' trivia, you realize a good number of the regular and recurring actors became very involved with their character. Especially people like Andrew Robinson, Armin Shimerman and J.G. Hertzler, who each wrote a whole novel about their characters Garak, Quark and Martok; or Nana Visitor, who met with the writers whenever she felt a scene was wrong about Kira. Another big name actor, René Auberjonois, consulted regularly with the writers (requesting a new uniform for Odo, etc.), though he was a little more subdued—even if he didn't particularly care for this or that plot development:
Ira Behr: Being the pro that he was, he sucked in whatever dismay he was feeling—though I still got some of those vibes. He didn't do a screaming, "I won't do it, I won't play it! No no no!"
"Rumpelstiltskin" was originally going to be a leprechaun who follows O'Brien around the station like a bad smell. A less-than-amusedColm Meaney (who had earlier endured an episode full of horrific Irish stereotypes in TNG's "Up The Long Ladder") made the writers change it.
According to Behr, Armin Shimerman was reluctant to go for broad humor since it went against his deep respect for the Ferengi. (One of Armin's old shames is his goofy and oddly racist turn as Letek in the TNG's "The Last Outpost", which cemented the Ferengi as the laughingstock of the galaxy.) Quark is often the odd man out in panto storylines such as "Ferengi Love Songs", "Profit and Lace", and "The Emperor's New Cloak". While the other Ferengi (Combs, Shawn, et al.) seem to be getting into the spirit of things, Armin's 'zany' dialog is delivered oddly straight.
"I could have gone one-dimensionally aggressive and mean and ugly with this character if I'd chosen to. I have the feeling that's what they kind of wanted. I thought, 'I've done that a hundred and fifty times already.'"
On his approach to playing the role, Ira Behr observed that Marc Alaimo reads every line like he's the hero of every episode he's in. "You listen to Marc talk about Dukat, and it's totally different than I see the character." The writers shrugged and let him carry on believing that, as it added some interesting flavor, but by Season 7 even Alaimo had fallen under Dukat's spell. He decided that Dukat's feelings for Kai Winn were genuine and that he would never strike a monk in a temple. Y'know, this guy who once declared the Bajoran religion a "superstition" and supervised the genocide on Bajor. Slugging a senior citizen over a book rental was beyond the pale for him.
Behr: In Marc's mind, I believe he felt his relationship with Winn was legitimate in some way, and that, in some wacky fashion, it was Dukat's bid for legitimacy. I mean Marc was actually upset when we had him hit Solbor. Until the very end, he wanted Dukat to be the hero of Deep Space Nine.
Ira Behr and Ron Moore got the itch to pursue a Kira/Dukat Foe Yay scenario (season 4's "Indiscretion", introducing Dukat's half-Bajoran love child Ziyal, is a clue to where things may have headed). Alaimo was all for it (what better way to secure a character's redemption than a romantic storyline with the female lead?) but Nana Visitor (Kira) flatly refused to do anything of the sort, pointing out that he was guilty of the brutal occupation and genocide of Kira's species. ("If you put a gun to her head, I don't think Kira would ever consider it.") Behr tried his best to jimmy the lock in various ways, such as forming a 'family unit' with Dukat, Kira and Ziyal during the Dominion occupation of Bajor. But in the end, Nana was unmovable. Finally, the storyline was handed off to Kira's mother Meru, who turns out to have been Dukat's "comfort woman" in "Wrongs Darker Than Death Or Night" (co-written by Behr).
Out of all the cast members, Michael Dorn probably had the most pull. After seven years of makeup calls, he wasn't interested in reprising his old role, but the showrunners were so desperate to have Worf cross over that they bent over backwards to make him happy. No longer would Worf be the big guy who got tossed around cargo holds!
Siddig wasn't too happy about his character being retconned into an Augment. He interpreted it as Behr/Berman et al. attempting to squeeze him into a "Data" role without consulting him, and responded by deliberately reading long equations and statistics in a drowsy, non-eloquent manner. The Augment stuff quickly faded into into the background and became all but irrelevant.
Word of Dante: Barry Jenner was mostly winging it while playing the Admiral Ross character. He decided that Ross was a conflicted family man whose son enlisted and died in Starfleet, twisting him into a Knight Templar who will stop at nothing to preserve the Federation. Internally, at least, he regrets dragging the DS9 crew (whom he admires) into his machinations.
Andrew Robinson has commented in multiple interviews that he considered Garak "omnisexual," and also strongly implied it in the character book he wrote. Robert Hewitt Wolfe has stated that he wrote Garak to be attracted to Bashir, but Bashir never realized this. And in the documentary What We Left Behind, Ira Stephen Behr flat out stated that Garak was obviously gay, and that it was a missed opportunity not to acknowledge and explore that.
Word of God: Ron Moore stated that although the background check in "Doctor Bashir, I Presume?" ended up marring Bashir's exemplary reputation, this didn't preclude him from being the new template for the Emergency Medical Hologram and — despite Dr. Zimmerman's complaints — he did actually end up being selected. Therefore fans assume that either the (unseen) EMH Mark III or Mark IV was based on Bashir.
Dax was benched (again) in "Rocks and Shoals " after sustaining injuries from the ship crash. Actually, Terry Farrell was suffering from a skin disorder which made her allergic to sunlight. This made it impossible to shoot scenes in the quarry, so she slept through the episode in a cave.
Armin Shimerman and Max Grodenchik had previously played Ferengi in TNG's "The Last Outpost" and "Captain's Holiday". Marc Alaimo also played the very first Cardassian, Gul Macet, in TNG's "The Wounded". (Word of God said that Macet and Dukat are cousins.) He also played one of the first Romulans to appear on TNG.
J.G. Hertzler, most well-known among DS9 aficionados for playing Martok, also played Sisko's soon-to-be-dead commanding officer, the Vulcan captain of the U.S.S. Saratoga in the pilot. He also later played changeling Laas in Season 7's "Chimera". This earned him the distinction of playing two Changelings in the show: Several times in the guise of Martok (before we meet the genuine, one-eyed one), and again as Laas. This also meant that he died twice, and possibly a third time after Laas contracted Section 31's virus.