AProcol 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 fashion, the only major surprises coming from the periodic lineup changes that added a new instrumental voice to the proceedings. At their most accessible, as on "A Whiter Shade of Pale" and "Conquistador," they were one of the most popular of progressive rock bands, their singles outselling all rivals, and their most ambitious album tracks still have a strong following.

The band's origins lie in the decision of Southend R&B band, The Paramounts, to call it a day in 1966. Looking for a new outlet, singer Gary Brooker was introduced by the legendary Guy Stevens, then an Island A&R man, to an as-yet-untried lyricist, Keith Reid. Quickly knocking out four songs for a Stevens-produced demo, the duo recruited some musicians and signed to Decca's new 'progressive' label, Deram. One of those songs was A Whiter Shade of Pale, which was released as a single in May 1967. Perfectly encapsulating the nascent "Summer Of Love", it featured a melody stolen from Bach, some beautiful Hammond organ from new boy Matthew Fisher and a set of wonderfully incomprehensible lyrics that sounded like Dylan without discipline. Within two weeks it was at #1 in the UK, where it stayed for six weeks, and on its way to selling four million copies worldwide.