Ellefsen previously played bass in the black metal band Emperor (1991–1992), prior to forming this project in 1993.

In the mid 90’s he had a brief spell playing in West Ham reserves, culminating in an incident where Harry Redknapp was confronted by angry fans.

He dismissed accusations of favouritism and comparisons to fellow youth prospect Scotty Canham and was quoted as saying ‘This goblin is going to the top.

It came about in 2001 when Mortiis was set to release The Smell of Rain, which was such a departure from his earlier records that he wanted to brand it in a way to signify this.

The last album of this era, The Stargate, went a step further by introducing a wider range of instruments including acoustic guitars, flutes and dark vocals; mainly provided by Sarah Jezebel Deva.

It was during this era that Ellefsen decided he needed to seek members to perform in a live setting, which later helped change how Mortiis as a band sounded.

[4] On 16 April 2007 Mortiis released a remix album titled Some Kind of Heroin, reworking material from The Grudge, via Earache Records.

"Some Kind of Heroin" offers diverse remix material including interpretations by a wide range of contemporaries, such as Zombie Girl, Gothminister, Implant, XP8, PIG, the Kovenant, Velvet Acid Christ, Girls Under Glass, David Wallace, Kubrick, Flesh Field, Victor Vortexx, Dope Stars Inc, In the Nursery among others.

Between 2011 and 2015, Mortiis (as a band or a solo musician) never stated that the project was on hiatus, although the last tour ended at P60 in Amstelveen (Netherlands) on 8 July 2011,[7] with no performance, recording or releases since.

The album (The Great Deceiver) was originally finished in 2008, and included mixes by Chris Vrenna (of Nine Inch Nails and Marilyn Manson).

The album was a reworking of his 1994 work Ånden som Gjorde Opprør, and was instigated after he was invited to perform at the 25th anniversary celebrations for former label Cold Meat Industry in 2017.

[15] For nearly the entirety of the band's existence, frontman Ellefsen has altered his facial appearance using several alternatives before using a prosthetic mask and ear set.

[citation needed] When talking about the influence for the imagery that his band uses, Ellefsen has commented, "A lot of people do not get that you can do more than just look like you're waiting for a bus.

Mortiis’ most notable credited remixes are for artists signed to the Belgian industrial label Alfa Matrix, including Zombie Girl (on the album Blood, Brains and Rock 'N' Roll) and I:Scintilla, another female fronted industrial metal act who released their album Optics featuring a bonus disc with remixes by Mortiis and other artists including Combichrist and Clan of Xymox.

[19] Mortiis has also provided remixes for Italian Industrial Rock/Metal bands including Dope Stars Inc., T3CHN0PH0B1A, as well as the American Ethereal/Neoclassical act Melankolia.

Having completed an album's worth of songs, Ellefsen commented at how they were "atmospheric and eerie" and also "very dark" while "some of it actually is semi-song structured, with some melody and sense to it."