When he was a teenager, Chun learned Judo and Karate while studying in Japan. Before the end of World War II Chun was approached by the head of the Yun Moo Kwan judo school and asked to teach karate there. He agreed, and also taught judo there. Since Chun was actively involved in martial arts instruction only between 1943 and 1950 there is little information about him. Chun helped lay the foundation, however, for what was to become taekwondo. Many of his students went on to become influential taekwondo pioneers themselves.