Metallica is an American heavy metal band from Los Angeles, California. The band's fast tempos, instrumentals, and aggressive musicianship placed them as one of the founding "big four" of thrash metal alongside Slayer, Megadeth, and Anthrax. Metallica formed in 1981 when James Hetfield responded to an advertisement that drummer Lars Ulrich had posted in a local newspaper. Since 2003, the line-up features rhythm guitarist and vocalist Hetfield, drummer Ulrich, lead guitarist Kirk Hammett and bassist Robert Trujillo. Previous members of the band are lead guitarist Dave Mustaine (who went on to found Megadeth), and bassists Ron McGovney, Cliff Burton and Jason Newsted. The band also had a long collaboration with producer Bob Rock, who produced all of its albums from 1990 to 2003 and served as a temporary bassist between the departure of Newsted and the hiring of Trujillo.