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.
Black metal
The term "black metal" was coined by the English band Venom with their second album "Black Metal" (1982). Although deemed thrash metal rather than black metal by today's standards, the album's lyrics and imagery focused more on anti-Christian and Satanic themes than any before it. Their music was fast, unpolished in production and with raspy or grunted vocals. Venom's members also adopted pseudonyms, a practice that would become widespread among black metal musicians.