Acoustic string band music in the country tradition comprises high, plaintive singing, fiddle, mandolin, five-string banjo, guitar and upright bass. The music spotlights tight harmony singing and improvisational instrumental solos. Thematically, the music can be either secular or sacred, but many important artists come from a gospel tradition. Widely regarded as the father of bluegrass, Kentucky native Bill Monroe was a vastly influential bandleader, chart-topping singer/songwriter, and innovative, virtuoso mandolin player. The 1946 incarnation of his Blue Grass Boys featured Earl Scruggs' pioneering five-string banjo playing and Lester Flatt's singing and guitar playing. They would all ascend to bluegrass legend and establish the paradigm for bluegrass to come -- namely the Stanley Brothers, the Osborne Brothers, Reno & Smiley, and Flatt & Scruggs. In the 1960s and '70s, a progressive element cropped up in bluegrass with bands such as the Kentucky Colonels, the New Grass Revival, Boone Creek, and many others augmenting the high-lonesome sound with elements of jazz, thereby broadening the canon to include songs from folk, rock and pop genres. And then there's the new traditional movement, which seeks to bring bluegrass back to its purist roots, ironically through newfangled production techniques. But the bluegrass we are referring to here encompasses the genre as a whole, with the heaviest emphasis on the genre's purist blueprints.