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 but their musical approach has changed over the years.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.