Wilytank
People attribute the formation of the first wave of black metal to Venom, Mercyful Fate, Celtic Frost, and Bathory. But of those four, Bathory is the only band that actually played black metal, and it is this band alone that should truly be credited for the start of this genre.
With their third album, Under the Sign of the Black Mark, Quorthon and his crew continue their storm of damnation that started with their monumental debut album and continued with their impressive though lacking second album. To many people elsewhere, Under the Sign of the Black Mark is the must have black metal Bathory album and rightly so.
The production here is better than the first two albums while still having that demented raw quality to it. The songs are still fast, furious and evil. There are some really insane guitar solos threw in here too, most notably in the outro to "Equimanthorn". Even the slower, longer song "Enter the Eternal Fire" is really awesome. In fact, I believe Darkthrone pay tribute to it (or rip it off >.> ) in their Under a Funeral Moon song "To Walk the Infernal Fields".
Of their pre-viking age era albums, Under the Sign of the Black Mark is Bathory's finest moment. Truly a pinnacle of the black metal genre.