Mike Compton is the mandolin. I first became aware of him and his incredible virtuoso flourishes in the Down From the Mountain concert film, which was an evening celebrating and performing the traditional music found in O Brother Where Art Thou.
In 2006 Compton and fellow mandolinist David Long put out an album of traditional blue grass numbers titled Stomp. The album is a celebration of bluegrass music with large sections of the album built out of the duelling instrumental melodies of the two performers. There's a particular focus upon the songs of Bill Monroe, the American musician widely credited with inventing the bluegrass genre (the name of the style comes from Monroe's band the Blue Grass Boys).
And so we have todays Best Song Ever: Compton and Long's powerful reading of Monroe's 'Evening Prayer Blues.'