Book excerpt: Robert Johnson was, according to Eric Clapton, "the most important blues singer that ever lived." An itinerant street musician, with a weakness for whisky and women, his is a life of pure legend-the man who sold his soul for the devil, and thereby invented modern music. Precious little is known about his 27 years, or the circumstances of his death, and even the site of his grave is contested. In this mini-biography, acclaimed music critic Chris Salewicz investigates the truth behind the myth, evoking an incisive profile of an enigmatic figure who, with just 29 songs, changed popular music for ever.