Kim Sun-Yung was a Karate master, particularly Tang Soo Do, in South Korea who trained John Kreese in the art of Karate. After Kreese went on to train his fellow soldier, Terry Silver, Silver and Kreese went on to continue their training with Sun-Yung in South Korea. It was mentioned in flashbacks from the Vietnam War during Kreese and Silver's time in the army by Captain Turner that Master Kim trained him during the Korean War.
As part of a conspiracy to ruin Miyagi-Do Karate, Terry Silver concocts a story of how John Kreese died, and how Kim Sun-Yung demanded Terry apologize to Mr. Miyagi for Kreese's cruel behavior during the 1984 All-Valley Tournament. However, this was all an elaborate hoax concocted by Silver to gain Daniel LaRusso's trust and let his guard down. However, it is unknown if Kim was apart of the conspiracy.