Issue 38 Orgll forms by Oerjan Nilse staes that the pioneer doing the most work was Nam Tae Hi.
Sadly I never got to ask Han Cha Kyo directly about this but his progeny claimed he was the primary contributor to this pattern. During a conversation with General Choi's son who counted GM Han Cha Kyo as one pf his first instructors, he confirmed this.
The Original Forms of Taekwondo article by Oerjan Nilsen. Hyung Ja Won. I double checked my reference materal at home, the closest I found was Ja on, but I still believe this is the Okinawan/Japanese Jion (also spelled Jaon) kata. David Hacker