Which guitarist was fired from Metallica and replaced by Kirk Hammett?

Dave Mustaine was the guitarist fired from Metallica and replaced by Kirk Hammett.

Mustaine joined Metallica in 1981 as its original lead guitarist, shortly after drummer Lars Ulrich and vocalist-guitarist James Hetfield formed the band in Los Angeles. He toured with Metallica and helped write material that later appeared on the band's early albums, although he did not play on a Metallica studio album.

Metallica dismissed Mustaine on April 11, 1983, after ongoing conflicts involving alcohol and drug abuse, aggressive behavior, and clashes with Hetfield and Ulrich. The band was preparing to record its debut album, Kill 'Em All, at the time. Mustaine was sent back to Los Angeles by bus and soon formed Megadeth, which became one of thrash metal's leading bands.

Kirk Hammett, formerly of the San Francisco thrash band Exodus, joined Metallica the same day Mustaine was officially fired. A common mix-up is confusing Mustaine with Jason Newsted or Cliff Burton, both of whom joined Metallica later in different roles.