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 critical acclaim with the 1986 release Master of Puppets some calling it 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. With this release the band expanded its musical direction resulting in an album that appealed to a more mainstream audience.

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 alienated some 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.

Metallica has released nine studio albums, two live albums, two EPs, twenty-two music videos and forty-three singles. The band has become one of the most commercially successful and influential heavy metal acts. With 90 million records sold worldwide, including 57 million in the United States, the band has won seven Grammy Awards, and has had four albums peak at number one on the Billboard 200. The band's 1991 album, Metallica, has sold over 15 million copies, which makes it the 25th highest selling album in the United States.