Bill Monroe helped create bluegrass in the '40s, yet some of his boldest recordings came during the folk revival of the early ‘60s. “Wheel Hoss” breathes fire, with mandolin and fiddle trading solos like jazz horns, while the African-American spiritual “Swing Low, Sweet Chariot” captures his genius for bold arrangements. Monroe also worked with flatpicker Doc Watson, infusing old-timey gems like “Foggy Mountain Top” with nimble string work.