Kim was undefeated in 13 bouts when he was assigned by the WBA as the world's number 1 challenger to world Lightweight champion Ray Mancini. Most of his contests prior to the Mancini bout, however, had been in his native country, against somewhat obscure opposition.
Kim had to struggle mightily to lose weight on the days prior to the bout so that he could weight in under the Lightweight's 135 pound limit, or, as they say in boxing, "make weight". In what could be described as an eerie coincidence, he wrote the message kill or be killed on his Las Vegas hotel room's mirror on the days before the bout.
Mancini and Kim met in an arena outside Caesar's Palace on November 13, 1982. In what many ringside observers have described as an "action-packed" fight, Mancini and Kim went toe to toe for a good portion of the bout, but by the latter rounds, Mancini began to dominate the young challenger. Spent and battered, Kim went into round 14 with little left and Mancini dropped him. He got up, but the fight was stopped and Mancini retained the title.
Minutes after the fight was over, Kim collapsed into a coma, and was taken to a hospital. Emergency brain surgery was done there to try to save his life, but that effort proved to be futile, as Kim lost his life 5 days after the bout, on November 18. The week after, Sports Illustrated had a photo of the fight on their cover, under the heading Tragedy in The Ring.
Not only did Kim lose his life after that fight, but the lives of many others who were involved were affected too: Mancini had to go through a period of regrouping, as he blamed himself for Kim's death. After friends helped him by telling him that it was just an accident, Mancini was able to go on with his career, but Kim's death would always haunt him. The bout's referee, Richard Greene, committed suicide on February of 1983, and so did Kim's mother, four months later.
Many reforms in boxing took place after this fight. The WBC, which was not the fight's sanctioning organization anyways, was the first one to step up and admit, during their annual convention of 1982, that many rules and areas concerning fighter's medical care before fights needed to be changed to improve a fighter's chance of surviving a fight. WBC president Jose Sulaiman declared that, immediately after the Mancini-Kim bout, the WBC and their medical advisors had conducted a study that revealed that most fighters get injured more severely during rounds 13, 14 and 15, so the organization immediately decided to reduce the number of rounds in their championship bouts from 15 to 12. The WBA and the IBF followed the WBC in 1987. When the WBO was formed in 1988, they immediately began operating with 12 round world championship bouts.
Apart from the round reduction, the years after Kim's death would bring such new implements on a fighter's check up before fights as electrocardiograms, brain tests, lung tests and other medical tests. As one boxing leader put it, "A fighter's check ups before fights used to consist of blood pressure and heart beat checks before 1982. Not anymore".
The story of Kim's life was taken to the big screen in his native South Korea: Director Kwak Kyung Taek directed the movie named Champion, and actor Yu Oh Seong starred as the fallen boxer.
Kim compiled a record of 13 wins and 1 loss, with 10 knockouts.