Wait a minute.....

Did I miss something? Or am I forgetting something? Who is Jang Gang in the end? I mean the late emperor performed the AoS and turned into Jang Gang and with Lady Dohwa had Jang Uk- that's fine BUT— who is the Jang Gang who blocked Jang UK's torrent of energy and then disappeared into thin air voldemort style? Did I miss something? Does he turn back into himself? 

It was the original Jang Gang.

He got help from Jin Mu and swapped their soles back.

That's how everything started. That how Jin Mu got to perform alchemy of souls