Formed in 1983, the group originally consisted of guitarists Eric Peterson and Derrick Ramirez, bassist Greg Christian, drummer Louie Clemente and lead vocalist Steve "Zetro" Souza.
[2] The group's lineup remained stable until October 1992, when Skolnick left due to musical differences and was replaced by Glen Alvelais, formerly of Forbidden.
[5] By April the following year, Bostaph had been replaced by former Exodus drummer John Tempesta,[6] and by early 1994 Alvelais' lead guitarist role had been taken over by James Murphy.
[7] After recording the band's sixth studio album Low, Tempesta left Testament to join White Zombie, with Jon Dette taking his place.
[12] In 1998, the group recorded The Gathering with returning lead guitarist James Murphy, former Death bassist Steve Di Giorgio and former Slayer drummer Dave Lombardo.
[18] After several temporary breaks from the group due to family issues, Allen left Testament in February 2004 and was replaced by the returning Paul Bostaph.
[20][21] In February 2005, it was announced that Billy and Peterson would be reuniting with Skolnick, bassist Greg Christian, and drummers Louie Clemente and John Tempesta for a European tour.