Bill Monroe (1911-1996) invented the bluegrass style. Monroe had gotten his start playing mandolin in a Chicago band with his brothers, but his great innovation was to revamp the Appalachian tunes of his Kentucky childhood with faster tempos and virtuosic soloing, a classic country pairing of something old with something new.
Monroe and his band, the Blue Grass Boys, became regulars on the radio barn dance program Grand Ole Opry in the 1940s. Bluegrass became a popular style of its own, and Monroe eventually was inducted into both the Country Music and Rock and Roll Halls of Fame. Monroe died in 1996, but bluegrass, his brainchild, is currently enjoying a full-on revival.