Metallica is an American heavy metal band formed in Los Angeles, California. The band's fast tempos, instrumentals, and aggressive musicianship placed them as one of the founding "big four" bands of thrash metal, alongside Slayer, Megadeth, and Anthrax. Metallica was formed in 1981 when James Hetfield responded to an advertisement posted by drummer Lars Ulrich in a local newspaper. The band's current line-up includes founders Hetfield (vocals, rhythm guitar) and Ulrich (drums), longtime lead guitarist Kirk Hammett, and bassist Robert Trujillo, who joined the band in 2003. Lead guitarist Dave Mustaine, who went on to found Megadeth, bassists Ron McGovney (demos only), Cliff Burton (the first three records, died in 1986), and Jason Newsted (from 1987 to 2001) are former members of the band. Metallica collaborated over a long period with producer Bob Rock, who produced all of the band's albums from 1990 to 2003 and served as a temporary bassist between the departure of Newsted and the hiring of Trujillo.

The band earned a growing fan base in the underground music community and won critical acclaim with its first four albums; the third album Master of Puppets (1986) was described as one of the most influential and heaviest thrash metal albums. Metallica achieved substantial commercial success with its eponymous fifth album—also known as The Black 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 a number of artists who filed a lawsuit against Napster for sharing the band's copyright-protected material for free without consent from any band member. 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 (2003) alienated many fans with the exclusion of guitar solos and the "steel-sounding" snare drum. A film titled Some Kind of Monster documented the recording of St. Anger and the tensions within the band during that time. In 2009, Metallica was inducted into the Rock and Roll Hall of Fame.