Memphis Minnie. She could not only sing but she could outplay any of her husbands.

And I disagree about the 12-bar form being only 30 years old (you didn't really mean that, did you Brad?). Most of the older bluesman used it a lot although they certainly felt free to vary it according to mood. It became necessary to standardize it more when the blues was transfered from a one- or two-musician form to a four or more musician form, so everyone would know when to change chords. Actually that is one of the things I find most appealing about the blues - the virtuosity and intensity of feeling that can be displayed within a very simple structure. The simplicity means that even a beginner can evoke the feeling, but a master can be as expressive as his or her ability allows, still staying within the framework.

Jon W.