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. These last two were later replaced from the band, in favor of Kirk Hammett and Cliff Burton, respectively. In September 1986, Metallica's tour bus skidded out of control and flipped, which resulted in Burton being crushed under the bus and killed. Jason Newsted replaced him less than two months later. Newsted 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 subgenre alongside 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 achieved substantial commercial success with its self-titled 1991 album, 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. With the release of Load in 1996, Metallica distanced itself from earlier releases in what has been described as "an almost alternative rock approach", and the band faced accusations of "selling out".

In 2000, Metallica was among several artists who filed a lawsuit against Napster for sharing the band's copyright-protected material for free without the band members' consent. A settlement was reached, and Napster became a pay-to-use service. Despite reaching number one on the Billboard 200, the release of St. Anger in 2003 disappointed some critics and fans with the exclusion of guitar solos, and the "steel-sounding" snare drum. A film titled Some Kind of Monster documented the recording process of St. Anger.