Heavy metal music
Critics disagree over who can be thought of as the first heavy metal band. Most credit either Led Zeppelin or Black Sabbath, with American commentators tending to favour Led Zeppelin and British commentators tending to favour Black Sabbath, though many give equal credit to both. A few commentators—mainly American—argue for other groups including Iron Butterfly, Steppenwolf or Blue Cheer. Deep Purple, the third band in what is sometimes considered the "unholy trinity" of heavy metal (Black Sabbath, Led Zeppelin, and Deep Purple), despite being slightly older than Black Sabbath and Led Zeppelin, fluctuated between many rock styles until late 1969 when they took a heavy metal direction.
Rock music
From the late 1960s the term "heavy metal" began to be used to describe some hard rock played with even more volume and intensity, first as an adjective and by the early 1970s as a noun. The term was first used in music in Steppenwolf's "Born to Be Wild" (1967) and began to be associated with pioneer bands like San Francisco's Blue Cheer, Cleveland's James Gang and Michigan's Grand Funk Railroad. By 1970 three key British bands had developed the characteristic sounds and styles which would help shape the subgenre. Led Zeppelin added elements of fantasy to their riff laden blues-rock, Deep Purple brought in symphonic and medieval interests from their progressive rock phase and Black Sabbath introduced facets of the gothic and modal harmony, helping to produce a "darker" sound. These elements were taken up by a "second generation" of heavy metal bands into the late 1970s, including: Judas Priest, UFO, Motörhead and Rainbow from Britain; Kiss, Ted Nugent, and Blue Öyster Cult from the US; Rush from Canada and Scorpions from Germany, all marking the expansion in popularity of the subgenre. Despite a lack of airplay and very little presence on the singles charts, late-1970s heavy metal built a considerable following, particularly among adolescent working-class males in North America and Europe.