Richard Dragon is the leader of a team of Green Arrow enemies known as the Longbow Hunters, and is one of the greatest martial artists in the DC universe. In the comics hes the son of a drug kingpin killed by Diggle, which leads to his training and return to try and defeat Arrow. It wouldnt be too difficult to imagine that theres a character from the show whos been killed that they could work into being his father, and his martial arts skills would definitely fit within the Arrow world and give a chance to display some impressive fight choreography. Weve already seen one of the comics Longbow Hunters - Brick - be defeated by Team Arrow, so now it could be the leaders turn to show up.