His name is derived from a creature in Egyptian mythology. Astennu first came to notice as the guitarist and songwriter for the Australian black metal band Lord Kaos. The band recorded both the demo "Path to My Funeral Light" and a full-length album Thorns of Impurity in 1995.
Astennu stayed in Norway and reworked some music he had written for Lord Kaos into songs for a solo project called Carpe Tenebrum.
The first Carpe Tenebrum album Majestic Nothingness featured Astennu on all instrumentation with vocals from Nagash of Dimmu Borgir and The Kovenant. lieutenant was released in 1997.
Later the same year, Astennu joined Dimmu Borgir on guitar, freeing Shagrath to concentrate on vocals. Astennu"s first recording with the band was the 1998 European Parliament "Godless Savage Garden".
He also contributed some guitar solos to the album Aggressor and the European Parliament "Triumph of the Blasphemer" by Nocturnal Breed, a band that also featured Dimmu Borgir"s other guitarist Silenoz.
A second Carpe Tenebrum album, Mirrored Hate Painting, again featuring Nagash, was appeared in 1999. Astennu"s second album, Spiritual Black Dimensions was released the same year, on 1 March. During the tour in support of the album, Astennu was fired from Dimmu Borgir and returned to Australia in late 1999.
Once back in Australia, Astennu worked as a live sound engineer for a number of bands on the Sydney heavy metal scene and also acted as mixer, engineer and producer on a number of albums and releases.
In 2002 he recorded and released a third Carpe Tenebrum album, Dreaded Chaotic Reign, this time performing vocals himself. Dreaded Chaotic Reign was a death metal album whereas previous Carpe Tenebrum recordings had been black metal.
In May 2003, Astennu returned to the live circuit with Sydney band Infernal Method, for whom he had been engineering for several months. Early the following year he and Infernal Method drummer Graham Goode joined a hardcore band called Stronger Than Hate but by the end of the year both that band and Infernal Method had disbanded.
Since then Astennu has not played live with a band but continues to work in the field of sound engineering.