Yong-Sool Choi (1904-1986), one of the most influential people in the development of modern Korean martial arts, was born in Chung Buk province in Korea. Choi's parents died when he was very young, and when he was eight or nine years old he was taken to Japan from Korea by a Japanese candymaker. Choi eventually became very homesick, he cried much of the time, and was eventually abandoned by the candymaker. He began to wander the streets as a beggar and was regularly assaulted by other children. A Japanese man notices Choi because of the unique situation he is in - being so young and having to beg for food and money. This man took Choi in and eventually adopted him. Before the adoptive father sent Choi to school to get an education, his name was changed to Tatujutu Yoshida. The attempt at education was not a successful one because Yoshida (Choi) did not speak enough Japanese to understand the teachers. He became disinterested in school work and often wound up in fights. Consequently, he was asked if he wanted to get a regular education or learn to fight. He chose fighting, and was enrolled in a Daito-Ryu Aiki-Jutsu (pronounced Dae-Dong-Ryu Hap-Ki-Sool, in Korean) dojo with Sokaku Takeda (1860-1943), were he trained for approximately 30 years. Sensing that Japan was loosing WWII, Yoshida (Choi) made plans to return home to Korea, and did so in the winter of 1945. Upon his return home, he changed his name back to Yong-Sool Choi.

Somehow during the trip home, Choi lost a piece of his luggage, which unfortunately contained his money and the certificates which were proof of his training with Takeda Sensei. Because of a lack of money, Choi decided to stay in Tae Ku rather than to return to his home in Chung-Buk. After a year of working as a bread salesman on the street, Choi managed to save enough money to begin raising pigs. In order to feed his pigs, he would get up early every morning and travel to the Suh Brewery Company to obtain free leftover grain chaff.

In 1947, Bok-Sub Suh, who was a black belt in Yudo and the president of the Suh Brewery Company, witnessed a fight from his second floor office window, where he watched in amazement as one man defended himself against several attackers, with little effort. He was very impressed and curious about what he had observed and sent his office clerk to bring this man to his office. The man turned out to be Yong-Sool Choi. Suh asked Choi what kind of martial arts he practiced. Without an answer to the question, Choi asked Suh to grab his lapel. When Suh grabbed the lapel, Choi easily executed an elbow lock and threw Suh to the floor. Suh immediately grabbed Choi's lapel again, and he was simply thrown to the floor a second time. After being defeated twice, Suh begged for Choi to teach him, promising him more free chaff, as well as paying him money for lessons. When Choi agreed, Suh prepared a dojang at the brewery where Choi then had the opportunity to teach what he had studied for so many years in Japan.

It was during the next few years that Choi would begin to establish himself as an outstanding and well respected martial arts instructor. He called his art Yoo Sool (Korean pronunciation of Ju-jutsu). A few minor modifications were made, but for the most part, he was teaching exactly what he had learned from Takeda Sensei. He did, however, slowly begin to ad techniques, including some kicks and weapons techniques.

In 1954, Bok-Sub Suh was involved in an incident where he defended his father, Dong-Jin Suh, who was up for election to the National Assembly. A fight ensued against a few gangsters, and using kicks learned through his training in Yoo Sool, Suh defeated the gangsters. After some thought, Suh decided to suggest to Choi that the name Yoo Sool, be changed to Yoo Kwon Sool, to represent the fact that besides joint locks and throwing techniques, they were also practicing strikes and kicks.

After the end of the Korean war, while Choi was still teaching Bok-Sub Suh, he opened his own private school at his house and began to teach a few other students. This was in 1953. Some of the students during this period had already founded, or have gone on to found their own martial art styles. These include, Hwang Kee (Tang Soo Do), In-Hyuk Suh (Kuk Sool Won), Dr. Joo-Bang Lee (Hwa Rang Do), and Han-Jae Ji (Hapkido)