Monotheist is the sixth and final studio album by Swiss extreme metal band Celtic Frost, released on 29 May 2006 by Century Media Records. It was the band's first release of new recordings in fourteen years.
Preparation and development work for the project had been ongoing since 2000. The first recording sessions for the album started in late October 2002. The band consisted of founding members Martin Eric Ain (bass/vocals) and Tom Gabriel Fischer (voice/guitars/keyboards), along with guitarist/producer Erol Unala, Fischer's long-time songwriting partner. Unala became an increasingly significant part of Celtic Frost during the songwriting.
Working titles for the album included Probe and Dark Matter Manifest.
Celtic Frost's earlier work melded elements of thrash metal and death metal. The sound of Monotheist has been described as difficult to reduce down specifics, as the songs vary from avant-garde metal to doom metal to "blackened thrash" to gothic metal to symphonic metal. The result is a wide-ranging but very dark heavy metal experience. Don Kaye at Blabbermouth called it "a monstrously heavy and oppressive slab of metal" which goes "into even heavier, blacker territory" than previous albums. Adrien Begrand of PopMatters said that the album was nearly a masterpiece of "brutally heavy" metal, "completely devoid of light." Eduardo Rivadavia of AllMusic noted more subtle touches such as the "instantaneously infectious melody" of "A Dying God Coming into Human Flesh", and the "haunting female voices" heard in duet with bandleader Tom Warrior on "Drown in Ashes".
Monotheist is a deathcore band from Orlando, Florida. Vocalist JJ Polachek is in the bands 7 Horns 7 Eyes and Ovid's Withering, of which, 7H7E, ranked their album on No. 1 on Metalsucks.com by Vince Neilsteins' Top 15 albums, and therefore stated that Monotheist is very similar to 7 Horns 7 Eyes.