Star Trek: Deep Space Nine, syndicated
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This is (so far) my very favorite Trek series. The most complex of any of them, I felt, and the darkest. Best acting, best writing, best stories, best characters, best concept, and everything. I'd also say it had probably my favorite opening theme music. (It was the first Trek series not to include opening narration before the theme, and while I'll always be a fan of that whole Starfleet motto thing, I didn't miss it.) Anyway, the series begins in 2369. After decades of Cardassian occupation of Bajor, the Cardassians are kicked out and Bajor asks the Federation to take over space station Terok Nor, which is renamed Deep Space Nine. Then a wormhole is discovered in the Bajoran Sector, the first stable wormhole ever discovered. Of course both the Federation and the Cardassian Union wanted to explore the other side of the wormhole, but now we had it. What luck!
Although eventually we would discover that on the other side of that wormhole, in the Gamma Quadrant, lay the huge and powerful Dominion, which would become the greatest threat to the Federation since the Borg. The station would acquire a warship called the Defiant, which had been designed to fight the Borg, but which would now be used against the Dominion. And of course there were always the relations between Cardassia and Bajor, very complex issues. And there were aliens living in the wormhole who the Bajorans had built a religion around. And there were evil pah wraiths. What else happened in the course of the series? Well, lots of stuff on holosuites, including baseball games and James Bondish fantasies. Plus Roswell was explained. And there were several Mirror Universe episodes, based on an old episode of the original series. I couldn't possibly say nearly enough about this show. But it really was brilliant, fun stuff.
The main characters were Captain Benjamin Sisko (though he started the series as a commander), my favorite Trek captain, who could do action, diplomacy, philosophy, anything. Bajorans called him the Emissary, a religious figure whose coming was prophesied long ago. This was not a position he was comfortable with in the beginning, but he eventually embraced it. Also there was Major Kira Nerys, a Bajoran woman who'd been in the resistance during the occupation. Though not a part of Starfleet, she was essentially second in command of DS9. Then there was science officer Jadzia Dax, a joined Trill. Jadzia was the most recent of I think like 8 hosts of the symbiont Dax, whose previous host had been Curzon, an old friend of Sisko's, as well as a friend of a few Klingons from the original series. And Miles O'Brien, along with Keiko and Molly, transferred from the Enterprise to be the station's chief operations officer (essentially the chief of engineering; Keiko and Miles would have their son, Yoshi, during this series). Odo, a changeling who'd been found and raised by a Bajoran scientist, and worked for the Cardassians during the occupation, and stuck around as chief of Bajoran security when the Federation took over. Quark, a Ferengi who ran a bar, casino, and holosuites, and who was constantly at odds with Constable Odo. Quark also had a brother named Rom, who was kind of naive, not all that bright, but fairly friendly, and... he had some Ferengi-ish qualities about him, but also some much more Federation-like ideas, at times. So as much as he cared for and respected his brother, and as much as Quark cared for him, they didn't always get along that well. And I think Rom eventually became an engineer or maintenance guy or something. And then, there was Dr. Julian Bashir, who became best friends with O'Brien. And... well, I won't mention certain things which would eventually be revealed about him. I suppose various things would eventually be learned about just about everyone, which I don't want to mention. Too spoilery.
Who else was there? Eventually Worf transferred to the station as strategic operations officer, around the time the Klingon-Federation alliance was temporarily broken. In season 7, Jadzia would be replaced by a new host for Dax, named Ezri. Sisko had a son named Jake, who would become a writer. Ben Sisko would eventually start dating a cargo ship captain named Kasidy Yates. Also in some of the Mirror universe episodes we'd see the mirror counterpart of Ben's late wife, Jennifer. Jake's best friend was Rom's son, Nog (who would eventually join Starfleet). Rom would eventually marry a Bajoran Dabo girl named Leeta, who had dated Bashir for awhile (Dabo is a casino game, btw). There was a tailor named Garak, who used to work for the Obsidian Order, a Cardassian spy agency. There was Gul Dukat, former prefect of Terok Nor, who showed up now and then. Eventually his illegitimate, half Bajoran daughter Tora Ziyal came to live on the station. There was a Vorta (a race that worked for the Dominion) named Weyoun who also made trouble for DS9, and during the Cardassian-Dominion alliance, worked closely with Dukat, as well as another Cardassian named Damar, who would become important. There was Michael Eddington, head of Starfleet security on the station, who eventually... well, that's another secret I won't give away. There was Winn Adami, a Bajoran vedek (sort of a priest), who later became Kai (chief Bajoran spiritual leader). She made plenty of trouble, too, though she was supposedly an ally. There was Vedek Bareil, who was definitely an ally, and later Shakaar Edon, former leader of Kira's resistance cell, who would eventually become Bajor's First Minister (political leader). There was an alien named Morn, who hung out at Quark's bar a lot, but never said anything. Um, a Klingon general named Martok worked with Starfleet for a while during the Dominion War. No doubt I'm forgetting any number of important recurring characters, but that should do for now.
I should probably say some more, but I can't think what, right now. Definitely very interesting stories, though, and way more moral ambiguity than any other Trek series....