Together with Bruce Day and Steve Warrior, he formed the seminal metal band Hellhammer in 1982. In late 1983, bassist and songwriter Martin Eric Ain joined Hellhammer and the line-up of Fischer, Ain and Day recorded an EP, Apocalyptic Raids, as well as a series of demos for the German label Noise Records before disbanding in May 1984. Fischer and Ain joined forces once again and formed Celtic Frost, an influential avant-garde metal trio, in June 1984. In 1985, Fischer was asked to co-produce and sing on the first demo, titled Death Cult, by fellow Swiss group Coroner. Fischer also wrote the lyrics for the recorded songs. Two of the members of Coroner formed part of Celtic Frost's road crew until 1986. In 1987, many conflicts within Celtic Frost led to a dissolution of the band, but several months later, Tom reformed the band with a completely new lineup. The band's 1988 release, Cold Lake, established a drastic change in Celtic Frost's music, but greatly disappointed most fans. Tom has stated many times that he takes the blame for the negative direction of Celtic Frost's music during this period, since he was too distracted with a personal relationship and let the other band members do what they wanted. Celtic Frost eventually disbanded in 1993. A year after Celtic Frost was laid to rest, Fischer formed the EBM/industrial rock project Apollyon Sun. In 2000, Fischer's book Are You Morbid?: Into the Pandemonium of Celtic Frost received many favourable reviews, including this from Record Collector: "Intelligent, humble, questioning, insightful – the cultured side of extreme metal". Sometime in 2001, Fischer and Martin Eric Ain met each other again and began writing music, with the aim of creating a new, dark and heavy Celtic Frost album in the vein of their work on To Mega Therion and Into the Pandemonium. The album, entitled Monotheist, eventually was released in 2006. Fischer also performed in Probot, Dave Grohl's collaborative project with various metal artists, on the song "Big Sky" in 2003. In 2005, Tom produced vocal and guitar tracks for a "gothicized" version of Slayer's classic "Black Magic" recorded by Los Angeles-based gothic rock band Hatesex. The track appeared on their debut album entitled "Unwant". Due to the 'internal conflict' within Celtic Frost, Tom left the band on 2 April 2008, and has launched a new band named Triptykon. In 2008, he played guitars and bass for the cover song "Set the Controls for the Heart of the Sun" from the 1349 album Revelations of the Black Flame and also co-mixed the album. In 2009 he co-produced their album Demonoir. In 2010, he was awarded in the Metal Hammer Golden Gods Awards for Inspiration. He currently plays an Ibanez H. R. Giger series Iceman guitar. He also uses an Ibanez Tube Screameroverdrive pedal. Fischer was ranked No. 32 out of 100 GreatestHeavy Metal Guitarists of All Time by Guitar World. Fischer is a vegan. He also states that he does not drink, smoke, or take drugs. Fischer was the personal assistant to H. R. Giger from 2007 until Giger's death. He was a close friend of Giger and his wife Carmen, and continues to be active for the Giger estate and as the co-director of the Museum HR Giger.
