What makes Under the Sign of the Black Mark by Bathory notable?

This album is notable for being one of the first to establish the sound and aesthetic of black metal, influencing countless bands in the genre. Its raw production and thematic focus on darkness and mythology helped set the template for future acts, marking it as a significant release in underground metal. Released in 1986, 'Under the Sign of the Black Mark' was Bathory's third studio album, following their influential debut and sophomore efforts. At this point, Quorthon, the band's mastermind, was solidifying his reputation as a pioneer of black metal, pushing musical boundaries and experimenting with Viking themes that would become synonymous with his later work.