Star Trek: 10 Things You Didn't Know About General Chang
2. One Of The Original Generals
In the Original Series, the episode Errand of Mercy sees the Federation face off against the Klingons during the short-lived war of 2267. Kor would have been the most notable name in the episode, while the expanded universe inserts Chang into the action as well.
By this point in his career, Chang was already a general. This is roughly 26 years before the events of Star Trek VI. While Kirk and Spock deal with Kor on the planet of Organia, Star Trek: Klingon Academy reveals that Chang was above the planet, commanding the Klingon fleet that was facing off against Starfleet.
The Battle of Organia was only prevented by the Organians themselves, who where highly advanced non-corporeal beings. They manipulated reality to make all of the Federation and Klingon weapons too hot to tough, which effectively disarmed both fleets. They then imposed the Treaty of Organia on them all, predicting that both powers would one day become friends. While Kirk and Kor scoffed at this idea, Chang flatly refused it, which would eventually lead to his involvement in Gorkon's assassination.