"South of Heaven" was the album that came after their big break, "Reign in Blood". They deliberately slowed down the tempo and used undistorted guitars to offset the high intensity of their previous album.
Slayer is a popular thrash band and considered to be one of the most important pieces of the metal movement in the 80s. They had heavy themes around corruption, murder, torture, and politics. They also were considered to be extremely anti-religious. They are known for their speed guitar and aggressive lyrics, and their drummer is known as the godfather of the double bass. Without Slayer, Metallica, Megadeath, and Anthrax we would not have the music we do today.