Historically a male, recent times have seen the emergence of female top dogs as well.
"I felt a little emasculated by that comment, but it's OK because I know she is joking."
*for male specific examples, see other definitions.
Person B: No, piss off you cunt. (cookthechef)
Person C: Hey, that's not nice Person B. Why sure, you Topdog, you can help me out with this. You are a real nice guy!