Choi later stated that he became a student of Takeda Sōkaku, and studied a form of jujutsu known as Daitō-ryū Aiki-jūjutsu (大東流合気柔術) while in Japan.

[5] Choi returned to Korea after the end of World War II and in 1948 began teaching his art at a brewery owned by the father of his first student Seo Bok-seob (서복섭; Suh Bok-sub).

[6] Choi Yong-sool was honored with the titles doju (도주; 道主), which can be translated as "Keeper of the way", and changsija (창시자; 創始者), which simply means "founder".

Choi made his way to Osaka as a beggar and, after having been picked up by police, was placed in a Buddhist temple which cared for orphans in Kyoto.

[11] Choi spent 2 years at the temple and had a difficult life there, not only in school but with the other children due to his poor Japanese language skills and his Korean ethnicity, which made him stand out in Japan.

[6] This matched the boy's temperament: Choi had a tendency to get into fights and he had an intense interest in the war scenes depicted in the temple's murals.

The temple monk (Watanabe Kintaro) was reputedly a friend of Takeda Sōkaku, the founder of the Daitō-ryū Aiki-jūjutsu system, which is a Japanese martial arts system emphasizing empty handed methods based upon the sword styles and jujutsu tactics in which Takeda was an expert.

Choi says he was taken to Takeda's home and dojo in Akita on Shin Shu mountain where he lived and trained with the master for 30 years.

Regardless of the circumstances of Choi's martial arts training, he returned to Korea after World War II and settled in Daegu, first selling sweets and later raising hogs.

[8][15] In 1951, Choi and Seo opened up the Daehan Hapki Yu Kwon Sool Dojang (대한 합기 유권술 도장; 大韓合氣柔拳術道場), the first formal school to teach the art.

[18] and Park Jeong-hwan (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.

[19][20][21] Doju Choi made a special 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, documented part of this historic visit on videotape, which is in the hands of Doju Chinil Chang.

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.

[22] Chang's intimate video interview (one of several over decades) with his teacher Doju Choi during his visit to New York City has been abused through numerous interpretations and translations.

[27][28][29] 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.