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.
Hard rock
By the end of the decade a distinct genre of hard rock was emerging with bands like Led Zeppelin, who mixed the music of early rock bands with a more hard-edged form of blues rock and acid rock on their first two albums "Led Zeppelin" (1969) and "Led Zeppelin II" (1969), and Deep Purple, who began as a progressive rock group in 1968 but achieved their commercial breakthrough with their fourth and distinctively heavier album, "In Rock" (1970). Also significant was Black Sabbath's "Paranoid" (1970), which combined guitar riffs with dissonance and more explicit references to the occult and elements of Gothic horror. All three of these bands have been seen as pivotal in the development of heavy metal, but where metal further accentuated the intensity of the music, with bands like Judas Priest following Sabbath's lead into territory that was often "darker and more menacing", hard rock tended to continue to remain the more exuberant, good-time music.