When we talk about Star Trek creators and behind-the-scene icons, it arguably goes Gene Roddenberry, Jonathan Frakes, and then Ronald D. Moore. Moore was one of the core writers in Star Trek during the golden years. Having worked on The Next Generation and then Deep Space Nine, Moore would be brought on to write the first two Next Generation films, Star Trek Generations and First Contact.
He was stellar at crafting a complicated, emotional, and entertaining science fiction series and film. His work on Helix, For All Mankind or Battlestar Galactica should go to show you that. One of the things that often gets overlooked, however, is how often he would kill off a character of grave importance.
Moore didn't ax characters at the same pace as a Walking Dead or Game of Thrones would, but he was far more willing to end a character's story than others. ScreenRant did a list of every character he killed,
Obviously, as the writer of Generations, he's now known as the man who truly killed James T. Kirk. This isn't entirely true, as William Shatner was looking to move on from the role, but the producers were hellbent on killing Kirk in the film one way or another. So the duty to write that scene fell to Moore.
As one of the primary names on Deep Space Nine, he also had a hand in killing of recurring Klingon character Gowron. The character appeared in 10 episodes and was referenced in dozens more, but his death was a nice wrap-up to the conclusion of Deep Space Nine. Not a core enemy for most of the show, his death came at a point where change was needed among the Klingons, and Worf was the one to do that change.
Yet, the death that hit the hardest was that of Vedek Bareil. Having appeared in seven of Deep Space Nine, Bareil was often seen as one of the least corrupted people from the religious side of Bajor's culture. He was a future love interest for Kira Neryse and someone who genuinely seemed to want to do good. It made his death all the harder to accept, as it came really out of nowhere.
It was just further proof that when Moore wanted to kill someone off, he knew exactly how to do it to make sure the audience felt the true impact of the moment.