Given the lack—perhaps permanent—of good hard data, most of what gets written about Robert Johnson runs along the same rutted paths: a few facts, a few conjectures, a threadbare reminiscence from one of the usual grizzled informants, and that’s about it—pretty thin gruel, especially considering the richness of Johnson’s music. It seemed wise to me, when I set out recently to write about Robert Johnson for Musician magazine—for the third or so time—to seek less traveled ground: Johnson’s impact on some of today’s most influential pop musicians.