Progressive Viking metal duo Enslaved formed in 1991, when Ivar Bjørnson and Grutle Kjellson were still teenagers. Habitually stretching songs well past the 10-minute mark and spinning tales about Norse mythology in ancient Norwegian, Enslaved became known for its sheer extremity in an already extreme scene — even though it spins black metal through a more melodic filter than any of its peers. Listen to "793 (Slaget om Lindisfarne)" from 1997's Eld for a working demo of the band's particularly weird brilliance. Thrumming metal doesn't appear until 11 minutes in, but the song's multiple sections and near-operatic themes enshrine Enslaved's rep as pacesetters of '90s progressive black metal.
Although the entire genre has arguably played itself out over the past decade, Enslaved continues to record and tour. Last year's Ruun even snagged a Norwegian Grammy. These days, however, most of the songs are performed in English, and the production has drastically improved. With songs slashed to a more digestible six minutes or so, Enslaved even appears willing to sacrifice some of its inaccessibility to make its very loud point.