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 hardcore
New York hardcore bands such as Agnostic Front, Warzone, Sick of It All, and the Cro-Mags and the thrash metal subgenre crossover thrash paved the way for heavy hardcore. Heavy hardcore emerged in the late 1980s and early 1990s with bands such as Killing Time, Madball, and Sheer Terror. In the and early 2000s, many other heavy hardcore bands, such as Hatebreed, Bulldoze, Shai Hulud, and Strife, all became prominent heavy hardcore bands. Heavy hardcore bands such as Terror and Death Before Dishonor gained cult followings in the