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 Anthrax, Megadeth, and Slayer. 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. Lead guitarist Dave Mustaine and bassists Ron McGovney, Cliff Burton, and Jason Newsted 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.