Choi Hong Hi
Yun later joined the Oh Do Kwan in Seoul, where he trained with E Jhoon Chang. There he began to learn and teach the International Taekwon-Do Federation (ITF) style of taekwondo. In 1968, Yun, with the encouragement of both Choi and Shim, came to Manitowoc, Wisconsin and began teaching taekwondo at Manitowoc YMCA as part of the ITF's effort to bring the martial art to the Americas. In 1970, Yun moved to Milwaukee, Wisconsin, and established the first taekwondo school in the city. In 1971, Yun's school was visited by Choi Hong Hi and Nam Tae Hi, who taught at the first of many seminars that they were to host. As of 2004, Yun's school had four branches, all located in the United States midwest.