After being fired from Metallica, guitarist Dave Mustaine founded Megadeth. Mustaine had joined Metallica in 1981 as lead guitarist but was dismissed in April 1983 after conflicts involving substance abuse, aggressive behavior, and clashes with James Hetfield and Lars Ulrich.
Returning to Los Angeles, Mustaine set out to create a band that could rival Metallica’s speed and intensity. He formed Megadeth in 1983, initially recruiting bassist David Ellefson and other musicians as the lineup developed. The group’s debut album, Killing Is My Business... and Business Is Good!, arrived in 1985 and established its technically demanding thrash-metal style.
The other choices are notable metal bands, but none fits this particular history. Death Angel and Testament emerged from the Bay Area thrash scene, while Overkill formed in New Jersey. Megadeth, founded in Los Angeles, ultimately became one of thrash metal’s “Big Four,” alongside Metallica, Slayer, and Anthrax.