I figure being famous can be within specific areas of expertise.
Being a dietitian I may know certain nutritionist who have become famous within the field of nutrition for their contributions. They are famous amongst those of us interested in the study of nutrition. They may have not become wealthy or world renown but their efforts are recognized within the circle of nutritionist.

Before I became involved in folk music I did not know who Rick Fielding was, but once I start to become more aquainted with other musicians and those within the folk community, it was very apparent to me that Rick's dedication & contributions to the music has reach a level of recognition that I would consider famous amongst the folk music community.
I guess that is how I define famous then, the contributions someone has made in their field.

Bonnie