Heavy Metal music was first developed in the late 1960's.
 When rock began turning back to softer, roots-oriented sounds in late 1968, acid-rock bands mutated into heavy metal acts
 Several American bands modified heavy metal into more accessible forms during the 1970s: the raw, sleazy sound and shock rock of Alice Cooper and Kiss; the blues-rooted rock of Aerosmith; and the flashy guitar leads and party rock of Van Halen

