Being known as a creative death metal band, Therion developed over the years (starting with "Beyond Sanctorum" in 1992) to become an avant garde act appreciated by a strong undergound audience. Their third and fourth albums were extremely experimental and there was a change of members in between all albums. The founder of the band, Christofer Johnsson remained the only original member and wrote the majority of the song material.

In 1996 their fifth album "Theli" was released and this is usually considered to be the breakthough album of the band. The style on Theli had changed into a symphonic opera metal with all kinds of influences, including 70's progressive rock, 80's heavy metal, oriental music and plenty more.

Member problems continued and the follow up "Vovin" (Therion's best selling record with over 125.00 copies sold in Europe) was recorded as Christofer's solo album, but still under the name Therion. This was the first record to include real orchestra and with the records "Deggial" and "Secret of the runes" the band has created a total hybrid between catchy metal music and opera/classic music. Since Deggial the lineup has been stable except for drummers.

In 2002 the band celebrated their 15 year anniversary by releasing the double live CD "Live in Midgard".

On the upcoming twin albums "Sirius B" and "Lemuria" the band has taken this concept even futher and 171 musicians and singers in total were involved in creating these ultimate progressions of symphonic music.