Metallica's original lineup featured James Hetfield (guitar/vocals), Lars Ulrich (drums), Ron McGovney (bass) and Dave Mustaine (lead guitar). Due to tensions between McGovney and Mustaine, McGovney left the band. Castro Valley-born bassist Cliff Burton was recruited as a replacement.
Mustaine and Hetfield had personality conflicts, with Mustaine later blaming the rivalry on the fact that "there was too much personality" in the band.
Mustaine was fired in early 1983, just prior to the recording of Kill 'Em All. Hetfield and Ulrich stated that they fired Dave because of his alcohol and drug problems, as well as his overly-aggressive behavior. Mustaine initially denied this, but in Metallica's 2004 movie Some Kind of Monster, Mustaine stated that he wished Metallica had told him to go to AA. After Mustaine's departure, Metallica recruited Hammett, who previously played for Exodus and was a one-time student of Joe Satriani. The band started recording Kill 'Em All with Hammett barely a month after him joining. Mustaine went on to form the band Megadeth, who also achieved multi-million selling success.