Deep Purple are an English rock band formed in London in 1968. They are considered to be among the pioneers of heavy metal and modern hard rock, although their musical style has varied throughout their career. Originally formed as a psychedelic rock and progressive rock band, they shifted to a heavier sound with their 1970 album Deep Purple in Rock. Deep Purple, together with Led Zeppelin and Black Sabbath, have been referred to as the "unholy trinity of British hard rock and heavy metal in the early to mid-seventies". They were listed in the 1975 Guinness Book of World Records as "the globe's loudest band" for a 1972 concert at London's Rainbow Theatre and have sold over 100 million records worldwide.

Black Sabbath were an English rock band formed in Birmingham in 1968 by guitarist Tony Iommi, drummer Bill Ward, bassist Geezer Butler and vocalist Ozzy Osbourne. They are often cited as pioneers of heavy metal music. The band helped define the genre with their first three albums Black Sabbath, Paranoid and Master of Reality (1971). Following Osbourne's departure in 1979, the band underwent multiple line-up changes, with Iommi being the only constant member throughout their history.