Notodden Death / Black Metal project ZYKLON is a revamping of EMPEROR guitarist Samoth's (a.k.a. Tomas Thormodsæter Haugen or 'Zamoth' as he is known with this project) ZYKLON-B project. The second album, February 2001's 'World Ov Worms' for Candlelight Records, was simply credited now to ZYKLON, thereby losing the direct reference to the holocaust gas at a time when Norwegian Black Metal was being put under the political microscope. Major participants included EMPEROR drummer Trym Torson (a.k.a. Kai Johnny Mosaker) colluding with Destructor of MYRKSKOG. The Dutch label Displeased Records also issued a limited edition vinyl variant of 'World Ov Worms'.

Guesting on the 2000 'World Ov Worms' album is the INFINITE DECAY and LIMBONIC ART credited Daemon (Vidar Jensen), ULVER's 'Trickster G' (actually frontman Garm) and the American fetish star Persephone. Bass guitar for ZYKLON is sessioned by Cosmocrator of SOURCE OF TIDE and MINDGRINDER.

Following their 2001 'Milwaukee Metalfest' appearance vocalist Daemon parted ways with the group. A bout of touring in North America would see Secthdaemon (a.k.a. Anders Eek) of ODIUM, FUNERAL, FALLEN and MYRKSKOG holding down vocal and bass duties.

Zamoth and Lars-Stian of SOURCE OF TIDE would be reported as uniting with former EMPEROR drummer Bård 'Faust' Eithun in an unspecified project. However, this proposition never materialised. Eithun would also be announced as scoring the lyrics for a new ZYKLON release. Trym hooked up with MYRKSKOG man Kshatriya's new DISIPLIN act in 2002.

A limited edition remix single, shared as a split release with RED HARVEST, surfaced in March of 2003. ZYKLON worked towards a sophomore album with producer Fredrik Nordström, 'Aeon', for September issue, these recordings marking the studio inauguration of Secthdaemon. Guest contributions for this opus were delivered by VOID's Ocd and RED HARVEST's Ofu Kahn with lyrical contributions from ex-EMPEROR man Faust. ZYKLON partnered with DARK FUNERAL and GOATWHORE for the 'Extreme The Dojo Volume 9' Japanese gigs in January of 2004. The band then lent support to ARCH ENEMY's February and March European dates. There would be little respite for Trym as the drummer stepped in as stand in member for SATYRICON's April US tour.

In June of 2004 both Zamoth and Trym, working with Cosmocrator of MINDGRINDER and Invictus from DISIPLIN, participated in recordings for a WINDIR tribute album to honour the memory of the late Valfar. ZYKLON set 'Disintegrate' as the working title for a 2005 album. Later that same year Zamoth and Trym re-activated EMPEROR but still forged ahead with plans for the next ZYKLON opus, recording at Akkerhaugen Lydstudios in November.

The group teamed up with ENSLAVED, 1349 and KEEP OF KALESSIN for a UK tour in September 2006. In January 2007 ZYKLON vocalist Secthdamon recorded a guest appearance on the 'Urge To Annihilation' demo from the Norwegian thrash band KILL ALL. Meantime, Destruchtor delivered a guest guitar solo for the 'Eryx' album by GLORIA MORTI, featuring on the track 'Sands Of Hinnom'.

BLOOD TSUNAMI partnered with ZYKLON for UK dates in May.