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.
Popular music of Birmingham
Critics disagree over which band can be thought of as the first true heavy metal band, with American commentators tending to favour Led Zeppelin and British commentators tending to favour Black Sabbath. Led Zeppelin formed in 1968 and was made up of two London-based musicians from The Yardbirds and two from the Birmingham-based Band of Joy, marking an explicit combination of the musical influences of the two cities. The Yardbirds had extended the instrumental textures of the blues through extended jamming sessions, but it was the influence of the Midlands-based musicians – drummer John Bonham and vocalist Robert Plant – that would provide Led Zeppelin's harder edge and focus, and bring a more eclectic range of stylistic influences. While it remained based in blues and rock and roll conventions, the music of Led Zeppelin blended these with extreme volume and a highly experimental melodic and rhythmic approach, forging a much harder and heavier sound. This combination of intensity and finesse in Led Zeppelin's output redefined both mainstream and alternative rock music for the 1970s, particularly in the United States, where they remain the fourth bestselling act in music history.