A rope-a-dopa is a person that you would figure to be a doper but they turn out to be a respectable individual.
Etiology is taken from the word Rope-a-dope which in short means to fake someone out.
Generally occurs when you see someone who you think is going to be ghetto, hood, white trash, or a loser and they turn out to be pretty decent, polite, well spoken, and/or professional.
Example: Guy A - "So, you're telling me Tim Lincecaum isn't a pothead and a loser?"
Guy B - "No man. He just has long hair so he kind of looks like a doper"
Guy A - "Man, that fool is a rope-a-dopa!"