Choi was born on March 2, 1942, in Daegu, Keishōhoku-dō, Korea, Empire of Japan.

He started training in the martial arts at the age of 12 because his father was concerned—he wanted his small, physically weak son to be able to protect himself in the war-torn streets.

Due to injuries sustained from his martial arts training he sought medical attention in the United States of America, moving in 1970,[6][7] and began to study different physical therapy techniques.

Since resigning from the post of Vice President under Choi's organization in 1991, Koo has remained a staunch opponent.

Koo dedicates a large portion of his website to disparaging Choi and his organization.