Lombardo's speed and aggression earned him the title of the "godfather of double bass" by Drummerworld
Slayer is one of the most influential bands in heavy metal history. Steve Huey of AllMusic believes the musical style of Slayer makes the band stronger than the other members of the "Big Four" thrash metal bands Metallica, Megadeth and Anthrax, all of which rose to fame during the 1980s. Slayer's "downtuned rhythms, infectious guitar licks, graphically violent lyrics and grisly artwork set the standard for dozens of emerging thrash bands" and their "music was directly responsible for the rise of death metal" states MTV, ranking Slayer as the sixth "greatest metal band of all time", ranking number 50 on VH1's 100 Greatest Artists of Hard Rock. Hanneman and King ranked number 10 in Guitar World's "100 greatest metal guitarists of all time" in 2004, and were voted "Best Guitarist/Guitar Team" in Revolver's reader's poll. Original drummer Lombardo was also voted "Best Drummer" and the band entered the top five in the categories "Best Band Ever", "Best Live Band", "Album of the Year" (for Christ Illusion) and "Band of the Year".
Music author Joel McIver considers Slayer very influential in the extreme metal scene, especially in the development of the death metal and black metal subgenres. According to John Consterdine of Terrorizer, without "Slayer's influence, extreme metal as we know it wouldn't exist." Kam Lee of Massacre and former member of Death stated: "there wouldn't be death metal or black metal or even extreme metal (the likes of what it is today) if not for Slayer." Johan Reinholdz of Andromeda said that Slayer "were crucial in the development of thrash metal which then became the foundation for a lot of different subgenres. They inspired generations of metal bands." Alex Skolnick of Testament declared: "Before Slayer, metal had never had such razor-sharp articulation, tightness, and balance between sound and stops. This all-out sonic assault was about the shock, the screams, the drums, and [...] most importantly the riffs."
Groups who cited Slayer among their major influences include Bullet for My Valentine, Slipknot, Gojira, Hatebreed, Cannibal Corpse, Pantera, Kreator, Mayhem, Darkthrone, System of a Down, Lamb of God, Behemoth, Evile and Lacuna Coil. Steve Asheim, drummer for Deicide, declared that "there obviously would not have been a Deicide as we know it without the existence of Slayer." Sepultura guitarist Andreas Kisser affirmed that "without Slayer, Sepultura would never be possible." Weezer mentions them in the song "Heart Songs" from their 2008 self-titled "Red" album. The verse goes: "Iron Maiden, Judas Priest, and Slayer taught me how to shred..." Dave Grohl recalled, "Me and my friends, we just wanted to listen to fucking Slayer and take acid and smash stuff."
The band's 1986 release Reign in Blood has been an influence to extreme and thrash metal bands since its release and is considered the record which set the bar for death metal. It had a significant influence on the genre leaders such as Death, Obituary, Cannibal Corpse, Morbid Angel and Napalm Death. The album was hailed the "heaviest album of all time" by Kerrang!, a "genre-definer" by Stylus, and a "stone-cold classic upon its release" by AllMusic. In 2006, Reign in Blood was named the best metal album of the last 20 years by Metal Hammer. According to Nielsen SoundScan, Slayer sold 4,900,000 copies in the United States from 1991 to 2013.