Therion, formerly known as Blitzkrieg (1987-1988) and Megatherion (1988), is a symphonic metal band founded by Christofer Johnsson in Upplands Väsby, Sweden in 1987.

Therion was initially a death metal band, however starting with 1995’s Lepaca Kliffoth, Therion began to gradually incorporate symphonic elements into their metal music. The band has seen many changes in line-up and style throughout its history with Christofer Johnsson being the only constant member.

Beginning as a death metal band, they later turned to combining orchestral elements with their metal music, employing heavy use of choirs and classical musicians, not only as additions to but also as integral parts of the composition. The band is one of the first both commercial and audience successful heavy metal with fully live orchestra featured. It is also one of the bands which originated, popularized and highly influenced the symphonic metal genre.

Therion takes its lyrical themes from various mythologies, occult and magical teachings, and ancient traditions and writings. The majority of the lyrics are written by Thomas Karlsson, head and founder of the magical order Dragon Rouge, of which Johnsson is a member. The band’s name originates from the Greek word therion (θηρίον), which means beast, in reference to the “beast” of the Christian Book of Revelation, though the word itself is taken from the Celtic Frost album To Mega Therion.