Star Trek: 10 Things You Didn't Know About Martok
7. He Nearly Got His Eye Back
When the real Martok first appears in the Jem'Hadar prison camp during In Purgatory's Shadow, the key difference separating him from his Changeling doppelganger is his missing left eye, likely caused by constant sparring for the training/entertainment of the Jem'Hadar.
Upon his return to active duty on the frontlines of The Dominon War, producer Ira Steven Behr suggested to Hertzler that they restore the eye, but Hertzler refused, saying that a Klingon warrior would not care how many eyes he had, and that it would serve as a reminder for Martok of what he had endured in that camp, spurring him on in his conflict with the Jem'Hadar who had taken his eye from him.
Although Hertzler has since admitted that the decision may have been influenced by Christopher Plummer's similarly monocular Chang in The Undiscovered Country, it was enough to convince Behr, and Martok didn't get so much as an eye patch for the rest of the war.