Mustaine has a reputation for having been in many feuds with other heavy metal musicians. Some of them include the following:


Metallica - Lars Ulrich and James Hetfield
The most well-known of these is his feud with Metallica, in particular with drummer Lars Ulrich and guitarist/singer James Hetfield. While he received songwriting co-credit on Metallica's first two albums, Mustaine claims to have co-written other Metallica songs, including "Leper Messiah," for which he was not credited. The original version of "The Four Horsemen" was called "The Mechanix" and appears in its original form on the first Megadeth album, minus the bridge Metallica added to it for Kill 'Em All. The song "FFF" on Megadeth's Cryptic Writings very much resembles "Motorbreath" while another tune on that album apparently lifts from "Wherever I May Roam". It has been said that Megadeth's "Hangar 18" and the instrumental "The Call of Ktulu" (written along with Cliff Burton for his interest in H.P. Lovecraft's Cthulhu Mythos) on Metallica's second album, which Mustaine is credited as co-authoring, bear similarities. This feud has waxed and waned over the years. Mustaine has said in interviews that Megadeth's Risk album was so named after Lars suggested in an interview that Mustaine should take more creative "risks" with his music (incidentally, the album was a critical failure). Shortly after the events of September 11, 2001, Mustaine and Ulrich sat down together — with a therapist and cameras present — to talk things through. The subsequent inclusion of the footage in the movie Some Kind of Monster re-ignited the feud, as Mustaine has reportedly withdrawn his permission to use the footage in the film. Ulrich later noted in Metallica's fanclub magazine So What! in late 2005 that each time Mustaine slams him in the press it seems to coincide with the release of a new Megadeth album.


Metallica - Kirk Hammett
Mustaine's replacement within Metallica by Kirk Hammett resulted in bad blood between the two. Even though he has stated he "doesn't care Kirk took my job", he also noted "at least I got to bang his girlfriend before he took my job — how do I taste, Kirk?".[3] He has also claimed that many if not all of the solos on "Kill 'Em All" were written by him and emulated note for note by Hammett, and in "The Art of Kirk Hammett" Kirk states that he was told to use Mustaine's existing solos as a guideline. In the Megadeth edition of Behind The Music, Mustaine stated that "now he sees how [Hammett] tries really hard" and "thinks he makes really good use of what talent he has" after stating earlier in that interview "I hear how much time James and Lars allowed him to solo, and said to myself 'God, he's horrible...' ". This feud has dropped off considerably in recent years, and Mustaine tends to direct his attention more on Hetfield and Ulrich.


Ex-Megadeth members - David Ellefson
Mustaine's decision to break up Megadeth in 2002 left all band members miffed and holding grudges, especially David Ellefson, who hinted about Mustaine faking the injury as an excuse to break up the band during an interview with Metal Sludge magazine. Ellefson had been, after Mustaine, the longest-serving member of Megadeth. Subsequently, the rift between the two founding members exploded, with the two camps exchanging lawsuits against each other. David Ellefson's action alleged that co-founding guitarist Mustaine breached their long-running partnership agreement. He claimed Mustaine wrongfully took the lion's share of the band's income (estimated at more than $200 million since 1984) for himself and cut Ellefson out of the band's music publishing and merchandise revenues. Ellefson also said that Mustaine libeled him in an online posting, seeking at least $18.5 million in damages. Mustaine's counterclaim alleges that Ellefson executed a settlement agreement in which he gave up his 20% interest in Megadeth. Mustaine maintains that the settle