Heavy metal music
Critics disagree over who can be thought of as the first heavy metal band. Most credit either Led Zeppelin or Black Sabbath, with American commentators tending to favour Led Zeppelin and British commentators tending to favour Black Sabbath, though many give equal credit to both. A few commentators—mainly American—argue for other groups including Iron Butterfly, Steppenwolf or Blue Cheer. Deep Purple, the third band in what is sometimes considered the "unholy trinity" of heavy metal (Black Sabbath, Led Zeppelin, and Deep Purple), despite being slightly older than Black Sabbath and Led Zeppelin, fluctuated between many rock styles until late 1969 when they took a heavy metal direction.
Death metal
English heavy metal band Venom, from Newcastle, crystallized the elements of what later became known as thrash metal, death metal and black metal, with their 1981 album "Welcome to Hell". Their dark, blistering sound, harsh vocals, and macabre, proudly Satanic imagery proved a major inspiration for extreme metal bands. Another highly influential band, Slayer, formed in 1981. Although the band was a thrash metal act, Slayer's music was more violent than their thrash contemporaries Metallica, Megadeth, and Anthrax. Their breakneck speed and instrumental prowess combined with lyrics about death, violence, war, and Satanism won Slayer a rabid cult following. According to AllMusic, their third album "Reign in Blood" inspired the entire death metal genre. It had a big impact on genre leaders such as Death, Obituary, and Morbid Angel.