Procol Harum is arguably the most successful "accidental" group creation -- that is, a band originally assembled to take advantage of the success of a record created in the studio -- in the history of progressive rock. With "A Whiter Shade of Pale" a monster hit right out of the box, the band evolved from a studio ensemble into a successful live act, their music built around an eclectic mix of blues-based rock riffs and grand classical themes. With singer/pianist Gary Brooker and lyricist Keith Reid providing the band's entire repertory, their music evolved in decidedly linear...