<human>:  What is the history and background of metal music?
<bot>: Metal music is believed to have its origins in blues-rock and psychedelic rock of the late 1960s and early 1970s. However, it properly emerged in the form of hard rock and heavy metal in the mid-1970s with bands such as Led Zeppelin, Deep Purple, Black Sabbath, and Blue Öyster Cult. In the mid-1980s, metal music saw the rise of genres such as thrash and death metal with bands such as Metallica, Slayer, Megadeth, Anthrax, and Pantera at their forefront. These bands continued to innovate and push boundaries and eventually created subgenres such as black metal, melodic death metal, and nu-metal in the 1990s. By the 2000s, metal music had become a major global phenomenon with underground and mainstream bands alike gaining millions of fans across the globe.