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.
Heavy metal genres
Christian metal emerged in the late 1970s as a means of evangelism to the wider heavy metal music scene, and was pioneered by American bands Resurrection Band and Petra and Sweden's Jerusalem. Los Angeles's Stryper achieved wide success in the 1980s. California's Tourniquet and Australia's Mortification led the movement in the 1990s. Rap metal group P.O.D. and the metalcore groups Underoath, Demon Hunter, As I Lay Dying, and Norma Jean (dubbed by Revolver Magazine as "The Holy Alliance") brought some mainstream attention to the movement in the first decade of the 21st century, achieving ranks in the "Billboard" 200.