Here’s a fairly loose arc but it’s a pretty interesting one that goes deeper than it might seem, which is why I’m pulling one particular character from the many to appear in Deep Space Nine, and somehow not even one most fans are going to think about.
A somewhat lost element of Star Trek lore is that the first Klingon to ever appear was going to be a recurring character if actor John Colicos hadn’t been so busy. Kor makes his debut in “Errand of Mercy,” and would have also shown up in “The Trouble with Tribbles” and “Day of the Dove” (the other major Klingon appearances of the original series) if Colicos had been available.
So his replacements (Koloth in “Tribbles” and Kang in “Dove”) instead make their debuts, and the three of them then resurface three glorious decades later in the Deep Space Nine second season gem “Blood Oath,” which also finally cements Jadzia Dax’s credentials as a formidable character after a fair bit of waffling and uncertainty.
Long story short, Kor is appropriately the last of these Klingons standing, and he becomes subject to a prolonged arc of deciding what makes an aging Klingon’s life worth living.
First he shows up in “Sword of Kahless,” in which he competes with Worf on a mad quest to discover the legendary warrior’s weapon. Here he gets to nudge Worf into having a working relationship with another Klingon, which would eventually lead to his bond with Martok.
Which...would kind of be bad news for Kor himself, as we learn when we see him for the last time in the seventh season episode “Once More Unto the Breach,” in which we learn Martok’s backstory and Kor’s domineering role in it, and as such more about Kor’s backstory itself.
But the episode resolves Kor’s later dilemma by giving him the belated warrior’s death he had long sought.
The short arc is, all the same, a remarkable opportunity for the franchise to give a full story to a character (and species) that might have seemed one-note initially. But that’s Deep Space Nine in a nutshell, both in its own regard and how it deepens the franchise as a whole, sometimes in quite surprising ways. In no other series to date has an effort been made to flesh out such a seemingly minor character from another series, let alone itself.