Which guitarist co-founded the heavy metal band Megadeth after leaving Metallica?

Dave Mustaine co-founded Megadeth after leaving Metallica. He formed the band in Los Angeles in 1983 and became its lead vocalist, primary songwriter, and lead guitarist.

Mustaine had joined Metallica in 1981 and performed on early demos before being dismissed in 1983. After returning to California, he recruited bassist David Ellefson and began developing a faster, more technically demanding style that became central to Megadeth's identity.

Kirk Hammett replaced Mustaine in Metallica, while Marty Friedman and Chris Poland were later Megadeth guitarists. Mustaine's history with both bands helped make him a central figure in the development of American thrash metal.