Which 1970 song by Black Sabbath is considered one of the first heavy metal songs ever recorded?

Black Sabbath's 1970 song 'Black Sabbath' is considered one of the first heavy metal songs ever recorded. The song, which was also the first track on the band's debut album of the same name, is known for its ominous and heavy sound, featuring a tritone or 'devil's interval' and dark lyrics about Satan and witchcraft.

The song's impact on music was significant, with many considering it to be the birth of the heavy metal genre. It was a departure from the popular music of the time, which was dominated by psychedelic and folk rock. The song's influence can be heard in the music of countless heavy metal bands that followed, and it continues to be a staple in the band's live performances to this day.