prominent top student who became crucial to the survival of Doju Choi's full system is Chinil Chang, the personally chosen second direct lineage Doju(Grandmaster) and the only man awarded the 10th Dan and the title of Doju directly from Doju Choi.
Students of importance who were trained by Choi during the later periods of his teaching were Kim Jeong-yoon, Kim Yoon-Sang (Hangul: 김윤상) who later went on to form his Hapki yusul organization. and Lim Hyun-Soo (Hangul: 임현수) who supposedly claims to teach only the core skills taught to him by his original teacher and then much later by Choi Yong-Sool without the additional techniques which were appended to the art by Choi's students such as Ji Han-Jae and Kim Moo-Hong. Park Jeong-Hwan (Hangul: 박정환), who trained under Choi for only three years, is one of the later students that opened a Hapkido school in America, several of which still function today.
Doju Choi did make his only trip to the United States in 1982, several years prior to his death to visit his highest ranked instructor Chinil Chang in New York City and to preside over the creation of the US Hapkido Association. Master Mike Wollmershauser who was the only American to have trained under Choi Yong-sool himself had documented part of this historic visit on videotape which is in the hands of the second direct lineage Grandmaster Doju Chinil Chang. Doju Choi's wishes in the end was to spread Hap Ki Do all over the world as well as to unite the art as one family, one branch, one heart, even though Doju Choi had realized at that point that the system had splintered into too many political and warring fractions for that to ever happen. It was more his wish to keep his original system intact and for the lineage to be passed in a complete manner to his second direct lineage successor which he accomplished beautifully. Master Wollmershauser attempted to spread this word of unity throughout the world until his death in December 2002. Doju Chang maintains the integrity and purpose of his mission while continuing to teach 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 developm