His appearance is unknown to many. He is seen by almost everybody in the dark, so that he's only seen in silhouette. However, most notice that he wears a suit. If seen doing magic, the red aura from his horn reveals his coat being white, but that is all that can be told.
His cutie mark is also unknown to many for reasons stated above. Rumors, however, say anything from it being staff, showing leadership, to not having one at all.
Ring Leader, though confident, is not a very social pony. He remains mostly in the dark to obscure himself. He's always willing to terminate any who get in his way. If he's going through with something, he's going through with it. He speaks well of everypony he works over. He's willing to talk to anypony, under his own discretion.
Ring Leader, as he claims, is a captain of the royal guard, but under a different division of the average captain. This division is for research in unconventional ways of defense. They were doing experiments with spoken word, when tragedy strikes in Canterlot, but that information can't be disclosed. It did require him to pick up his research. He builds an underground vocal studio in an unknown location to test his conclusions and see if he can save the Equestrian royalty.