The Guinness Record holding "world's loudest band" Deep Purple started in 1968, and charged forward to become pioneers of heavy metal. The band originated as a musical project where members would come and go, making contributions and moving on if necessary. The band did indeed have a high turnover rate, which meant that Deep Purple's sound morphed as different artists added their influence. There are numerous eras of the band, each having a slightly different lineup and sound.
The first era of Deep Purple, known as Mark I, was when the band first experienced commercial success with their debut album Shades of Deep Purple. The band released two subsequent albums and toured extensively. They performed dramatic covers of songs as well as original compositions, including songs with strings and remarkable battling guitar and organ duels.
The 'classic' Deep Purple lineup is considered to be the Mark II era that went from 1969 to 1973. The band was comprised of singer Ian Gillan, guitarist Ritchie Blackmore, bassist Roger Glover, drummer Ian Paice, and keyboard player Jon Lord. They released In Rock, which put the band at the forefront of heavy metal, a digression from their previous orchestral collaborations. Gillan had a powerful voice that complemented Deep Purple's hard new sound. The band's most famous song, "Smoke on the Water", was released in this era, written about a casino that burnt down during a Frank Zappa concert. The Mark II lineup was revived in 1984 and 1992, with many other lineups and albums released in between.
Presently, the Mark VIII lineup is in effect, with Ian Paice as the only original member left in Deep Purple. It is a real possibility that the project will keep moving on and that Deep Purple will continue putting out new albums and touring with a revolving lineup of innovative musicians.