Top 20 Musicians of All Time, in Any Genre: #10-6

10. Guido D'Arezzo

Simply put, the writings of Guido D'Arezzo (above) laid the foundations for Western music. This medieval theorist of the 11th century was the dude responsible for inventing the notation we still use today. In other words, without him we wouldn't have sheet music. Oh yeah, and you know that mnemonic "do-re-mi-fa-so-la-te-do"? He invented that too. -Chris Walker

According to folklore, Robert Johnson made a deal with the Devil in order to gain mastery of the guitar. Hell, no matter how he got it, the Mississippian has influenced pretty much every rock musician you love. Keith Richards said he was as good as the blues can get, Eric Clapton called him the most important blues musician that ever lived, and he's considered one of the greatest guitarists of all time. Supposedly poisoned at the age of 27 in 1938, he never lived to enjoy public recognition nor commercial success. -Rebecca Haithcoat