Chang is a mainstay of Korea's roster in The King of Fighters series. His name literally means "giant man" in Korean—fitting, since he's massive and fights with a ball and chain like several other KOF characters.
He started out as a serious criminal with a violent streak, the kind of guy who actually scared people. Kim Kaphwan spotted him on prison surveillance footage and decided Chang's raw strength would be perfect for his personal crusade to fight injustice. Never mind that Chang broke out of prison without much trouble—Kim caught him anyway and forced him into his infamous "Rehabilitation Project."
That's where Chang met Choi Bounge, another convict trapped in Kim's program. The two initially plotted their escape together, but eventually they actually bonded and stopped planning to leave. (Some observers have been skeptical about how genuine this friendship is, but they seem genuinely comfortable with each other now.)
By The King of Fighters XI, both Chang and Choi had convinced Kim to join the Garou Team. They show up in the team's ending at PaoPao Cafe celebrating their victory. Interestingly, once Kim officially declared them "rehabilitated," Chang and Choi started worrying—not about themselves, but about whoever Kim targets next. They know exactly what his program entails, and they're not sure the next batch of criminals will have as easy a time of it.
Content compiled by AnimeList.moe from publicly available sources.