Joni Mitchell

Joni Mitchell! She's a warblesome folkstress with a voice like molten gold. "They paved Paradise, and put up a parking lot," she once mused, oblivious to the parking needs of Paradise's ever-swelling population.

But Joni's life has not - as you might expect - been one long bed o' folksome roses. She caught polio as a kid, which weakened her left hand; consequently, she plays guitar chords in unusual shapes and tunes her guitar weirdly. This led to her distinctive, somewhat jazzy sound.

So there you go! Polio. It killed a lot of kids, but it also progressed folk music. FACT.