Metallica /m??tæl?k?/ is an American heavy metal band from Los Angeles, California, formed in 1981. Founded when drummer Lars Ulrich posted an advertisement in a local newspaper, Metallica's line-up has primarily consisted of Ulrich, rhythm guitarist and vocalist James Hetfield, while going through a number of bassists. Currently, the spot is held by Robert Trujillo. 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 during the genre's development into a popular style. The band earned a growing fan base in the underground music community and critical acclaim, with the 1986 release Master of Puppets described as one of the most influential and "heavy" thrash metal albums. The band achieved substantial commercial success with Metallica (1991), 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.