Metallica is an American heavy metal band that formed in 1981 in Los Angeles, California. Founded when drummer Lars Ulrich posted an advertisement in a Los Angeles newspaper, Metallica's original line–up consisted of Ulrich, rhythm guitarist and vocalist James Hetfield, lead guitarist Dave Mustaine, and bassist Ron McGovney. McGovney and Mustaine were later ejected from the band, in favor of Cliff Burton and Kirk Hammett, respectively. The ejection of Mustaine has subsequently resulted in a feud between him and Metallica. Mustaine later went on to form Megadeth. In 1986, Metallica's tour bus skidded out of control, and Burton was crushed under the bus and was killed. Jason Newsted replaced him, although he left the band in 2001 and was replaced by Robert Trujillo in 2003.

Metallica's early releases included fast tempos, instrumentals, and aggressive musicianship that placed them as one of the "Big Four" of the thrash metal genre alongside with Slayer, Megadeth and Anthrax. The band earned a growing fan base in the underground music community, and some critics say the 1986 release Master of Puppets is one of the most influential and "heavy" thrash metal albums. The band rose to fame with its 1991 self–titled album Metallica, which debuted at number one on the Billboard 200. Some critics and fans believed the band changed its musical direction to appeal to the mainstream audience.