The martial arts style portion of Lion Do is primarily rooted in Moo Lim Do (there is much more to Lion Do than just the martial arts style, though).  Moo Lim Do is a Korean style that incorporates pieces of several other Korean martial arts, chief among them Taekwondo, Tang Soo Do, and Hapkido, with Hapkido the dominant contributor.  It was created by Korean Grand Master Kap Chul Lim (Master Lim).

Before it was known as Moo Lim Do, Master Lim previously taught his style as Kuk Sool Wan Hapkido.  One of our Lions Academy Judges (Kim Mangum) was trained in it at the time of the transition, and he still has his old Kuk Sool uniform and patch, and you can see below:

Korean Hapkido in turn was originally created by Master Choi Yong-Sool (Taekwondo was created by Master Choi Hong-hi, and both individuals are widely known as "Master Choi", but they are different individuals, so don't confuse them).   

Both Master Lim as well as another contemporary, Master In Hyuk Suh (Master In), were trained under Master Choi (the creator of Hapkido).  Master Choi created many training locations, and rotated various senior students in to teach when Master Choi could not be there.  Both Master Lim as well as Master In were students under those floating instructors, and usually were not directly under Master Choi.  But they were both under Master Choi's umbrella.

When Master In was under Master Choi, he created "Kuk Sool Won Hapkido", not as a separate Hapkido, but as a unique identifying name for the Hapkido schools that he was working with.  It is my understanding that Master Choi gave his blessing to Master In to use that name, and Master Lim also adopted it for a short time.

Then Master Choi died, leaving Master In as the custodian of the name that he created.  Since he was the creator of the name, he owned it and could do as he wished with it. Master In chose to change the name to simply "Kuk Sool Won™", and also chose to break connection with his Hapkido roots.   Master In then went on to turn "Kuk Sool Won™" into an international organization, boasting over 1.3 million members, and over 800 schools worldwide in 27 different countries.

Notice the trademark symbol with "Kuk Sool Won™".  With the legal registration that Master In created, Master Lim was faced with a dilemma-- either quit using the name and adopt a different name, or join Master In's organization as a subordinate.  Master Lim chose to abandon the "Kul Sool Won Hapkido" name, and chose to go under the name "Moo Lim Do", which means "The Way of Lim's Martial Art", which is a family name.  This transition occurred in the 1980's.

I imagine that Master In felt that the path he took was the cleanest path forward for maximizing the growth of his efforts, as a clean break likely held fewer legal considerations than attempting to negotiate something else with his contemporaries.  But some have felt it was a betrayal of his roots.

Much of Moo Lim Do can be found in Kuk Sool Won™, but the two branches have many philosophical differences.  Master Lim sought to strip things out to bring Moo Lim Do down to it's bare essence, and Master In sought to put more things in, in an attempt to create (quoting from their website) "a systematic study of all of the traditional fighting arts, which together comprise the martial arts history of Korea".

Since much of the martial arts aspect of Lion Do is rooted in Moo Lim Do,and since much of Moo Lim Do can be found in Kuk Sool Won™, we might occasionally use Youtube clips of Kuk Sool Won™ to illustrate aspects of Lion Do.

Members Trained in Moo Lim Do
(Red Belt or Higher):

Picture taken 2017
Back Row: Dalton Strong, Isaac Pratt, Daniel Pratt, Nevin Pratt, Denise Pratt, Jacob Pratt, Jessica Gustafson, Linda Green
Middle Row: John Pratt, Olivia Pratt, Luke Pratt, Kyle Pratt, Eliza Pratt, Byron Pratt, Jeremy Winters
Front Row: Master Il, Master Lim