h his students as he has since arriving in the United States decades ago.
Choi's claims of being a student of Daito-ryu under Takeda Sokaku are contested and unsupported by the fee and attendance records of Takeda Sokaku which still exist today. However, since Choi was Takeda's house servant, others claim it is logical to assume he was trained by him or at least in his dojo. While staying in Japan, Choi is said to have taken on a Japanese name and was known as Asao Yoshida (吉田朝男) according to a posthumously released interview, or Yoshida Tatujutsu according Seo Bok-Seob. The claim by some that the lack of documentation was due to his Korean ancestry is difficult to uphold since other Korean students are mentioned in the records. Still there is a strong similarity to the techniques taught in Daito-ryu and the techniques of hapkido.
Argued also is the source of the name hapkido for the art which Choi Yong-Sool's student, Ji Han-Jae, claims to have coined the name for the art. Seo Bok-Seob however states in a 1980 interview that it was Jung Moo Kwan who first used the term to refer to the art as well as the symbol of the eagle to represent the art.
A direct student of Choi, Chinil Chang inherited the title of Doju in Choi's personal and complete system of Hapkido on January 15, 1985, becoming the second direct lineage Grandmaster.
On April 5, 1985 Choi personally awarded Chang the only existing 10th Dan certificate in Hapkido history. Chang also had the privilege and honor of being the first Hapkido master awarded the 9th Dan certificate by Choi in 1980.
A large inauguration ceremony followed on April 11, 1985. The historic event was covered and documented by Korea Sports News and MBC Korean Television. Choi Young-sool, Chang, and Choi's son, the late Choi Bok-Yeol, were in attendance. Chang is the only Hapkido master ever awarded the 10th Dan and Doju title directly from Choi. Choi left the full documentation and recordings of the system to Chang, who continued to research and document the full history and development 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