Hellhammer was a Swiss extreme metal band from Nürensdorf, active from 1982 to 1984. Although the band's sound and style were heavily criticized and poorly reviewed during their active years, they have been widely praised in retrospect and are often regarded as a key influence on black metal. In June 1984, Hellhammer disbanded but two of its members soon formed the influential extreme metal band Celtic Frost.

Inspired by the music of Black Sabbath, Venom, Raven, Motörhead and Angel Witch, guitarist/vocalist Thomas Gabriel Fischer (a.k.a. "Tom Warrior"), bassist/vocalist Urs Sprenger (a.k.a. "Savage Damage" and "Steve Warrior") from the band Grave Hill, and drummer Pete Stratton (Peter Ebneter) formed Hammerhead (later Hellhammer) in May 1982. Although Fischer "was not into punk at all," he was "blown away" by the Discharge records Why and Hear Nothing See Nothing Say Nothing, which profoundly influenced his music from then on. As he noted, a lack of extreme metal at the time meant that fans of Venom and Motörhead often had to resort to punk bands for similar sounds. GBH and Anti-Nowhere League also proved influential.

After the exit of Stratton and drummer Jörg Neubart (a.k.a. "Denial Fiend", "Bloodhunter" and "Bruce Day", from the band Moorhead) joining in the ranks in autumn 1982, Hellhammer attempted to find proper rehearsal spaces, which proved difficult due to either exceedingly high rents or unavailable studio hours. In June 1983, the group recorded their demo tape, Triumph of Death, for a mere $70. Despite being embarrassed by the end results, Hellhammer shipped their demo to a number of heavy metal magazines, such as Great Britain's Metal Forces; critical response toward them was generally favorable. Although rejected by the labels they sent tapes to, the band eventually caught the attention of a newcomer German label, Noise Records.

Steve Warrior was dismissed in the summer of 1983 due to lack of musical talent, and replaced first by Mike "Grim Decapitator" Owens (Mike Baum) from the band Violence. Schizo drummer Stephen Priestly from Wallisellen replaced Bruce Day in October 1983, and later in 1983 fellow Schizo member, American born Martin Eric Ain replaced Owens on bass, a change which marked the beginning of a serious and radical transformation in the band's music and lyrics. Finally still in 1983 Bruce Day rejoined to replace Priestly completing the Warrior / Ain/ Day line-up that recorded Hellhammer's only commercial release, Apocalyptic Raids in March 1984. After the EP was recorded, guitarist Vince "Dei Infernal" Caretti joined Hellhammer, after future Celtic Frost guitarist Oliver Amberg declined the offer. These changes were ultimately responsible for Fischer's and Ain's increasing perception of being limited within the confines of the purposely primitive Hellhammer vehicle. Hellhammer officially disbanded on May 11, 1984, and Fischer and Ain formed a new band under the name of Celtic Frost in June.

At the dawn of the next decade Noise Records released a new version of Hellhammer's debut, retitled Apocalyptic Raids 1990 A.D. This re-issue was augmented by two tracks off the Death Metal compilation, which was "something we always wanted to, even back in '84", claimed Tom Warrior. This re-release also came with a new cover design done by Martin Ain.

In November 2007, Tom Gabriel Fischer announced that the original master tapes of Hellhammer's demos (Death Fiend, Triumph of Death, and Satanic Rites) would be released as a 2CD/3LP package, titled Demon Entrails, in February 2008 with new liner notes on the complete history of Hellhammer, unreleased photos and artwork, and all tracks remastered personally by Tom Gabriel Fischer, Martin Eric Ain and Steve Warrior. The album was released by Prowlin' Death/Century Media Records.

In 2016, both Century Media and Prowling Death Records joint released an unreleased 7" vinyl single the band originally recorded in 1983 titled Blood Insanity. Tom Gabriel Fischer explained that the band contemplated releasing material they recorded at the time of the Triumph of Death demo sessions which would contain two songs. Unfortunately, the single languished into an unrealized state until the band's split, rendering any plans for future releases redundant. Fischer went on to say that it never left his mind since then and presented the idea of releasing the single to Century Media, in which the record company agreed.

Although its former members felt proud of Hellhammer's legacy by the end of the 1980s, that was not always so. In fact, Tom Warrior feared that his prior commitment to Hellhammer could hinder the future of Celtic Frost. A 1985 Kerrang! review summed up his worst fears: "The truly execrable Hellhammer may now have turned into Celtic Frost but still suck on the big one."