The clues: In the clue video, the Dragon makes reference to wearing funky costumes. They also not that their fire was dangerous early in their career, but they learned to calm down later in life. At the end, there are a few glimpses of medals, trophies, and the Statue of Liberty.
Who it could be: Given all the medals, the most obvious guess is that the Dragon is an Olympian. While Ken Jeong threw out Michael Phelps's name, others guessed DMX because of the "X" and dog bone featured in the video as well as Busta Rhymes for the "dangerous" reference, which is a name of one of his songs.