Reign in Bloo is the third studio album and major label debut by the American thrash metal band Slayer. Released on October 7, 1986, the album was the band's first collaboration with record producer Rick Rubin, whose input helped the band's sound evolve. Reign in Blood was very well received by both critics and fans, and was responsible for bringing Slayer to the attention of a mainstream metal audience. Kerrang! magazine described the record as "the heaviest album of all time", and a breakthrough in thrash metal and Speed metal.