Any serious Hapkido Player can tell you who is considered the original founder. There are a few people out there who have tried to take credit, but it is to late to BS a large portion of the HKD community. If you really want to learn about HKD then visit HKD forums. http://www.hapkidoforum.com/index.php
Try this one. There are some very knowledgeable people here. As for our origin, past Choi there are several great practitioners that have taken HKD to the next level and that is kinda where the list came from. As for myself, my Gm studied under Choi for a long time, but received his 9th dan under Ji. The HKD my Gm teaches is his flavor, his interpretation so I would have to check other. The basic/core techniques and principles of HKD are pretty much the same where ever you go. It is each teachers interpretation and preference of execution of techniques that differ.