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.
American popular music
In the early 1970s, the first major American bands began appearing, like Blue Öyster Cult and Aerosmith, and musicians like Eddie Van Halen began their career. Heavy metal remained, however, a largely underground phenomenon. During the 1980s, a pop-based form of hard rock, with a party-hearty spirit and a glam-influenced visual aesthetic (sometimes referred to as "hair metal") dominated the music charts, led by superstars like Poison, Bon Jovi, Mötley Crüe, and Ratt. The 1987 debut of Guns N' Roses, a hard rock band whose image reflected the grittier underbelly of the Sunset Strip, was at least in part a reaction against the overly polished image of hair metal, but that band's wild success was in many ways the last gasp of the hard-rock and metal scene. By the mid-1980s, as the term "heavy metal" became the subject of much contestation, the style had branched out in so many different directions that new classifications were created by fans, record companies, and fanzines, although sometimes the differences between various subgenres were unclear, even to the artists purportedly belonging to a given style. The most notable of the 1980s metal subgenres in the United States was the swift and aggressive thrash metal style, pioneered by bands like Anthrax, Megadeth, Metallica, and Slayer.