ent of Hapkido.
Furthermore, the future Grandmaster, who was a personally trained, closed-door disciple of Choi, was given Letter of Appointment certificates, the second dated December 1, 1977 and the third dated March 5, 1980. This gave Chang more progressive power and authority in Choi's Hapkido Association. These specific certificates, along with his 9th Dan ranking in 1980, and 10th Dan ranking in 1985, amply demonstrate that Choi was grooming Chang to be the future Grandmaster of Hapkido. 
Chang's intimate video interview with his teacher Doju Choi during his visit to New York City has been abused through numerous interpretations and translations. Some have even claimed erroneously to have conducted the interview themselves, further clouding and distorting the truth and gravity inherent in the interview. These endless distortions were generally rebutted in various media each time they appeared.
Doju Chang continues to teach in New York City after decades of maintaining a commercial school, as well as a stint teaching Hapkido at the United Nations. He currently teaches a small group in NYC dedicated to the preservation of Hapkido. Many detractors have spread endless conjecture about him. One lineage created further controversy by stating Choi passed the system to his only son, Choi Bok-Yeol, which is incorrect, misleading, and insulting to the legacy and wishes of Choi. Black Belt Magazine, respecting Chinil Chang as the second lineage successor, asked him to write a brief obituary on Choi that appeared in the April 1987 issue.
Many people have claimed to be students of Choi Yong-sool, and it is often hard to verify whether or not these claims are valid. This is a list of people who were long time students of Choi.
- Chinil Chang (the second direct lineage Grandmaster was awarded the only 10th Dan in Hapkido and the title of second direct lineage Doju by Dojunim Choi on January 15, 1985.)
- Seo Bok-Seob (Hangul: 서복섭; Choi's first student in 1946)
- Ji Han-Jae (Hangul: 지한재; student #14 of Choi in 1955, Founder of the Korea Hapkido Association and Sin Moo Hapkido, and Sung Moo Kwan in Andong)
- Kwon Tae-Man (Hangul: 권태만; First founder of a hapkido dojang in Incheon)
- Kim Yong-Jin (Hangul: 김용진; Founder of the Ulchi Kwan)
- Myung Jae-Nam (Hangul: 명재남; Founder of Hankido and Hankumdo)
- Oh Se-Lim (Hangul: 오세림; former president of Korea Hapkido Federation)
- Myung Kwang-Sik (Hangul: 명광식; Founder of the World Hapkido Federation)
- Kim Moo-Hong (Hangul: 김무홍; Choi's student in 1955, Founder of the Korean Hapkido Association and Shin Moo Kwan in Daegu)
- Moon Jong-Won (Hangul: 문종원; Choi's student in 1955, Founder of Won Moo Kwan in Busan)
- Kim Yoon-Sang (Hangul: 김윤상; Founder of Hapki yusul)
- Yoo Byung-Don (Hangul: 유병돈; Han Kuk Jeong Dong Hapkido, Orthodox Hapkido)
- "합기도 ①" at Doosan EnCyber & EnCyber.com (두산 백과사전) (Korean)
- "합기도 ②" at Doosan EnCyber & EnCyber.com (두산 백과사전) (Korean)
- "합기도 ③" at Doosan EnCyber & EnCyber.com (두산 백과사전) (Korean)
- "합기도 ④" at Doosan EnCyber & EnCyber.com (두산 백과사전) (Korean)
- (Korean) 허인욱의 무인이야기 장보고와 정년 그리고 송징
- Hentz, Eric (editor), Taekwondo Times Vol. 16, No. 8. Tri-Mount Publications, Iowa 1996. "The Beginning of Hapkido; An Interview with Hapkido Master Seo, Bok-Seob" by Mike Wollmershauser.
- Kim, He-Young. Hapkido (alternately The Hapkido Bible). Andrew Jackson Press, Baton Rouge, Louisiana 1991.
- Posthumously Released Interview with Choi Yong-Sool (1982).
- Scott Shaw (1996). Hapkido: Korean Art of Self-Defense. Boston, Massachusetts: Tuttle Publishing. ISBN 0-8048-2074-0.
- Pranin, S. (1988). Aikido Journal, AikiNews, 77. Interview with Kisshomaru Ueshiba: The Early Days of Aikido.
- http://www.segye.com/Articles/NEWS/CULTURE/Article.asp?aid=20100216002847&subctg1=&subctg2= (Korean)
- (Korean) 이소룡과 대결했던 합기도고수 지한재 방한 세미나 2010.01.12 chosun.com
- Kim, Jeong-Yoon. Personal interview with Matthew Rogers. Seoul. 1995.
- Spiedel, Rod. "Yong Sool Kwan; History of the Hapkido Hapkisul Headquarters". Taekwondo Times. Nov. 2006/Vol.26. No.6. Article compiled by Barrie Restall.
- Stepan, Charles 