666 might be the number of the beast, but over 20 is where Iron Maiden sits as far as members to have played in the band - and that number fails to take into account touring musicians. Notable membership changes over the years have included multiple singer swaps, with Blaze Bailey filling in for the legendary Bruce Dickinson for most of the 90s. Prior to Dickinson, who joined in 1981, vocal duties were covered by Paul Day, Dennis WIlcock, and Paul Di'Anno (who was the first vocalist to actually record with the band). With all the turmoil it's a wonder that Maiden have been as successful as they have been. Up the irons!