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: The Story of Metal
This part focuses on the rise of the new wave of British heavy metal, the Soundhouse in London, and the beginning of the L.A. scene with Van Halen. It also talks about Ronnie James Dio's influence on the birth of the "devil horns" and metal's leather fashion brought on by Rob Halford. Bands discussed include Judas Priest, Iron Maiden, Van Halen, and Def Leppard.