England's Deep Purple is bona fide classic rock royalty with a body of work spanning nearly seven decades. Along with Cream, Black Sabbath, and Led Zeppelin, they defined hard rock and early heavy metal. Though their lineup has constantly evolved, Deep Purple effectively made music a career for guitarist Ritchie Blackmore, bassist Roger Glover, vocalists Ian Gillan and David Coverdale, drummer Ian Paice, and organist/composer Jon Lord. Shortly before his death in 2012, Lord attributed Deep Purple's success in selling more than 100 million albums to "musical restlessness." Thei...