Would a 4th dimensional character be one that grows significantly from one aspect we observe them at the first time we meet them to a completely different aspect over time? A shift in perspective and not a minor but major shift?
I'm not sure but maybe the 4th dimensional character is one we shape simply by observing it, our expectations and observations somehow change that character. Maybe its our perspective of said character rather than the actual character itself? I don't know how to put it right, but I think I'm hitting the topic in a blindfolded dart tossing manner...