It depends wildly on the scenario. In some cases I'm almost invisible, in others almost too forceful.
If it's a social group/gathering? "The Silent One." Pretty much without exception.
If it's a functional/theoretical discussion (work, school)? "The Leader", "The Challenger", or "Information Resource", depending on the situation. Usually I tend to take charge out of impatience, if nothing else.
If it's a group to do something physical (sports, group construction projects, etc.) "The Worker Bee"