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 metal music
During the 1980s, glam metal became popular with groups such as Mötley Crüe, Poison and Def Leppard. Underground scenes produced an array of more aggressive styles: thrash metal broke into the mainstream with bands such as Metallica, Slayer, Megadeth, and Anthrax, while other extreme subgenres of heavy metal such as death metal (with bands such as Death, Possessed, and Obituary) and black metal (with bands such as Mayhem, Bathory, and Immortal) remain subcultural phenomena. Since the mid-1990s popular styles have further expanded the definition of the genre. These include groove metal (with bands such as Pantera, Sepultura, and Lamb of God) and nu metal (with bands such as Korn, Slipknot, and Linkin Park), the latter of which often incorporates elements of grunge and hip hop.