The naming of the band
The band's name is drawn from the word megadeath, referring to the destructive capability of a nuclear weapon. Dave Mustaine explained that he came across the word in a handbill by Senator Allan Cranston discussing the dangers of nuclear arms. When Dave read the words "power of megadeath can't be rid...", it immediately appealed to him: "I thought, 'What a fantastic name.' It represents extreme power which is how I view my music.".
So, contrary to the thinking of many, his naming of the band is not a call for Armageddon, but a reference to the impact he wanted to make through his, and the band's, music.
Quote from http://www.woodstock.com/html/biow0105.shtml