Star Trek: 10 Production Secrets You Never Knew About Klingons
8. They Were Created By Gene L. Coon As A One Time Villain
When it came to the occupying force on the Planet Organia, Gene L. Coon conceived of a race who would be a one-time-only villain, like the Salt Vampire, the Kelvans, and the Mugatu, some of whom would come later in the show. Organia was designed to be a simple, Medieval village that required saving, when in fact it would end up as something completely different.
The Klingons would serve as the Russians in this episode, with the Federation serving as the Americans in what was to be a Cold War-inspired story.
The introduction of the Klingons in this episode resulted in the destruction of the Enterprise. That is to say, part of it. Only the bridge set was used in Errand Of Mercy, so some of the standing Enterprise sets were demolished to make way for Organian sets. Like the Klingons, the Organian sets were meant to appear once and be done. For the Organians, that did prove the case (bar a cameo in Enterprise) but for the Klingons, it was very different.
D.C. Fontana was not a fan of the Klingons returning to the franchise repeatedly. She found the Romulans to be far more interesting, yet their appearances would be much more sporadic.