He was Uncle Pen incarnate, a snowy-haired, almost Biblical figure championing the purity of the music he created, seemingly poised to smite anyone who dared sully it. Six years after his death, that has become Bill Monroe's image beyond the bluegrass world. It's understandable, since in those later years, he abandoned his public introversion to become a regular on cable's old Nashville Network and an honored guest on others' records. The bluegrass he created has taken on near-epic status. While musicians and musicologists know better, facile romanticists obsessed with the mystique of the High Lonesome Sound rhapsodize over ancient British tunes becoming Appalachian ballads and, through Monroe's vision, into bluegrass, born in mist-shrouded Kentucky ridges and meadows. That same bucolic iconography has long graced bluegrass LP covers. The truth, of course, is that Monroe's music was both worldly and fluid. Had it been static, far removed from the mainstream, it would never have evolved and flourished as it had to. Proof of that resides in this superbly packaged, stunningly remastered six-disc collection. The fourth of Bear Family's Monroe boxes (the others cover the Decca years), it offers the complete 1936-38 Monroe Brothers recordings and the Blue Grass Boys' output from 1940-1949, including 50 unheard/unissued alternate takes. Kentucky roots notwithstanding, Bill and Charlie Monroe perfected the Monroe Brothers' duet sound at Chicago's WLS "National Barn Dance", where Bill sopped up inspiration from, among others, the Prairie Ramblers' aggressive rhythms. Even when they moved to the Carolinas, their style owed little to brother duos such as the Blue Sky Boys. They established themselves with gospel (their best-selling "What Would You Give?"), traditional tunes and a few covers. Their rendition of Preston Young and Buster Carter's 1931 recording of "Roll In My Sweet Baby's Arms" launched that song toward immortality. Fine, honest harmonies, spiced by Bill's high-velocity mandolin, abound, yet these recordings contained few flashes of bluegrass. Early strains of the new appear near the end as Bill adds blue mandolin licks to a cover of the Prairie Ramblers' "Rollin' On" and "Sinner You Better Get Ready". Blues had been ingrained in Bill since he worked with black guitarist-fiddler Arnold Shultz as a teenager in Kentucky. Indeed, one later Blue Grass Boy spoke of his boss' fondness for Howlin' Wolf, which makes more sense than it might seem. It took Bill nearly two years after the Monroe Brothers' 1938 split to firm up the direction revealed on the 1940 Blue Grass Boys sessions. A landmark for acoustic stringbands, his immortal rendition of "Mule Skinner Blues" and the gospel quartets revealed something both old and new. The mandolin showcases "Tennessee Blues" and "Honky Tonk Swing" reveal that Monroe's listening habits encompassed jazz and, given his stately cover of Bob Wills' "I Wonder If You Feel The Way I Do", western swing. Like Wills, Monroe established a formula that featured his sidemen as much as himself. As those sidemen came and went, the band became a vital incubator comparable to the Texas Playboys or the Jazz Messengers. Some hires were borne of necessity. Sally Ann Forrester's accordion on the 1945 sessions might seem apostatic, yet Monroe hired her during World War II, when he and other bandleaders faced a wartime musician shortage. He drilled syncopation into his uptempo numbers. "Rocky Road Blues" and "Blue Grass Special", remastered here in stunning clarity and depth, ratify his influence on Presley, Perkins, Feathers and other rockabillies. Nor was he averse to lifting from others. The intro to "Heavy Traffic Ahead" came note-for-note from Bob Wills' 1936 arrangement of Memphis Minnie's "What's The Matter With The Mill". His 1945 hirings of singer-guitarist Lester Flatt and, later that year, banjoist Earl Scruggs created quantum leaps from the 1940 band. Flatt's peerless singing offered Monroe a new and impressive foil for harmonies. His propulsive guitar, combined with Scruggs' fluid banjo and Chubby Wise's fiddling, created a new rhythmic paradigm. But that didn't happen overnight. Bluegrass historian Dave Samuelson notes that early 1946 Opry airchecks reveal Scruggs still seeking his rhythmic level. By the Columbia sessions in October, he, Flatt and Monroe were so in sync that bassist Cedric Rainwater, freed of anchoring the beat, played more creative lines. The joint departure of Flatt and Scruggs in 1948 was a blow to Monroe (he was estranged from them for decades), yet he rebounded well by 1949 with the equally impressive vocals of future bluegrass icon Mac Wiseman ("Can't You Hear Me Callin'"), the underrated Rudy Lyle's blues-drenched banjo rolls, and Monroe's roaring, modal "Blue Grass Stomp". Depending on the artist and material, studio chatter on reissues can be revealing or annoying. These alternates and even the flubs (known as breakdowns) reveal much about the precision Monroe demanded. Hearing Flatt and Monroe, one after the other, screw up the lyrics on "The Old Cross Road" and Monroe clearly snapping "that ain't no good like that, dammit!" does as much to humanize and demystify him as any biography. The saga continues today. Sharp divisions still divide the long-contentious bluegrass community as to the purity of one act, style or another. One faction stands for progress, others are in the middle, and a few meticulously re-create the "classic" sound as theater. If nothing else, this remarkable collection reveals that bluegrass in the hands of its creator was a work in progress -- even at the beginning.