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.
Nu metal
Joel McIver acknowledged Korn as the band that created and pioneered the nu metal genre with its demo "Neidermayer's Mind", which was released in 1993. McIver also acknowledged Korn as the band that started the new wave of American heavy metal, which is a heavy metal music movement that started in the 1990s. The aggressive riffs of Korn, the rapping of Limp Bizkit, and the melodic ballads of Staind created the sonic template for nu metal. The origins of the term "nu metal" are often attributed to the work of producer Ross Robinson, who has been called "The Godfather of Nu Metal" between producers. Robinson has produced for nu metal bands such as Korn, Limp Bizkit and Slipknot. Many of the first nu metal bands, such as Korn and Deftones, came from California; however, the genre soon spread across the United States and many bands arose from various states, including Limp Bizkit from Florida, Staind from Massachusetts, and Slipknot from Iowa. In the book "Brave Nu World", Tommy Udo wrote about the nu metal band Coal Chamber, "There's some evidence to suggest that Coal Chamber were the first band to whom the tag 'nu metal' was actually applied, in a live review in Spin magazine."