Star Trek: 10 Times Chief O'Brien Suffered
7. Tribunal
Tribunal, while not the earliest O'Brien Must Suffer episode was certainly one of the starkest examples of the man being tortured. The design of the episode, led by Herman Zimmerman, was based on George Orwell's 1984. It is also the first appearance of Cardassia Prime in Deep Space Nine, with the planet being shown as quite grim, and spartan.
The episode's plot sees O'Brien arrested and tortured by the Cardassians, charged with a crime he didn't commit. The titular tribunal is a show trial, with the verdict already decided long before he was ever brought to the planet.
The episode's inspiration came from a line spoken by Dukat in the episode The Maquis. There, he explained that on Cardassia, the verdict is always known before the trial begins, and it is always the same. It was to highlight that all trials are, in fact, demonstrations of the futility of defying the state. This is a theme that would follow Cardassians throughout the run of Deep Space Nine in particular.
It was also the episode to introduce the fact that Cardassians often use disguises and surgery to place their spies in other forces, with both Seska in Voyager and Dukat in the final season being other examples of this.