Deep Purple are an English rock band formed in Hertford in 1968.
 The band is considered to be among the pioneers of heavy metal and modern hard rock, although their musical approach changed over the years.
 Originally formed as a progressive rock band, the band shifted to a heavier sound in 1970.
 Deep Purple, together with Led Zeppelin and Black Sabbath, have been referred to as the "unholy trinity of British hard rock and heavy metal in the early to mid-seventies".
 They were listed in the 1975 "Guinness Book of World Records" as "the globe's loudest band" for a 1972 concert at London's Rainbow Theatre, and have sold over 100 million albums worldwide.
Rainbow (also known as Ritchie Blackmore's Rainbow or Blackmore's Rainbow) are a British rock band led by guitarist Ritchie Blackmore, active from 1975 to 1984, from 1993 to 1997, and from 2015 to the present.
 They were originally established with Ronnie James Dio's American rock band Elf, but after their first album, Blackmore fired the backing members and continued with Dio until 1979.
 Three British musicians joined in 1979, singer Graham Bonnet, keyboardist Don Airey, former Deep Purple bassist Roger Glover, and this line-up gave the band their commercial breakthrough with the single "Since You Been Gone".
 Over the years Rainbow went through many line-up changes with no two studio albums featuring the same line-up.
 Other lead singers Joe Lynn Turner and Doogie White would follow, and the project consisted of numerous backing musicians.
 A pioneer to power metal, the band's early work primarily featured mystical lyrics with a neoclassical metal style, but went in a more streamlined, commercial direction following Dio's departure from the group.
Acrassicauda is an American-based Iraqi heavy metal band formed in 2001.
 It is often credited as being the first heavy metal group to emerge from Iraq.
 The original band consisted of three Arab members and one Assyrian (Tony Aziz Yaqoo).
 The band formed and played concerts under the regime of Saddam Hussein.
 It became well known outside of the local Iraqi metal scene after Vice magazine did a profile of the band.
 It received even greater coverage when it was profiled in a feature-length documentary about the band and its troubles in Iraq called "Heavy Metal in Baghdad".
 The band's first album was released on March 9, 2010.
Kekal (sometimes stylized as KEKAL) is a heavy metal and electronic music band formed in 1995 in Jakarta, Indonesia.
 According to AllMusic, Kekal was one of the first heavy metal bands from Indonesia to make international inroads, and according to sociologist of heavy metal, Keith Kahn-Harris, was one of the few extreme metal bands from Southeast Asia to ever make more than a minimal impression on the global scene.
 Founded by two musicians known simply Yeris and Newbabe, the band underwent some shifts in lineup in its early years, but emerged with a consistent lineup of three key-members, guitarist/vocalist Jeff Arwadi, bassist Azhar Levi Sianturi, and guitarist Leo Setiawan.
 Frequently labeled as black metal, progressive metal, and avant-garde metal, Kekal plays a very diverse range of music styles within the frame of metal and rock, incorporating many other music genres such as ambient, electronic, jazz fusion, and progressive rock.
 Over the course of its career, Kekal has transitioned from a heavy metal-based style to a more experimental and electronic sound.
Joe Lynn Turner (born Joseph Arthur Mark Linquito, August 2, 1951) is an American singer, guitarist, songwriter, and producer.
 He is known for his work in the hard rock bands Rainbow and Deep Purple.
 During his career, Turner fronted and played guitar with pop rock band Fandango in the late 1970s; and in the early 80s, he became a member of Rainbow, fronting the band and writing songs with guitarist, Ritchie Blackmore and bassist, and producer, Roger Glover.
 After Rainbow had disbanded (the first time) in March 1984, he pursued a solo career, released one album, Rescue You, and then later did session work, singing background vocals for the likes of Billy Joel, Cher, and Michael Bolton.
 On the advice of Bolton, Turner began recording jingles for radio and television.
 Other songs he had composed or through collaboration with songwriters like Desmond Child and Jack Ponti were being recorded and released by international recording artists Jimmy Barnes, Lee Aaron, and Bonfire.
 Turner had a short-lived association with neoclassical metal guitarist Yngwie Malmsteen and then Deep Purple.
 From the mid-1990s, he resumed his solo career, releasing an additional nine studio and two live recordings.
 Turner did other session work, appearing as lead vocalist on tribute albums and working on projects involving various musical groups including progressive rock band Mother's Army; Bulgarian hard rock band Brazen Abbot; funk rock duo Hughes Turner Project; and classic rock/ progressive rock band Rated X.
 In 2006, Frontiers Records approached Turner to become involved with the AOR side project Sunstorm.
 By 2016, four albums under the Sunstorm name had been released.
 That same year, Turner released "The Sessions" via Cleopatra Records featuring a veritable who's who of classic rock royalty as guest musicians, before resuming his seemingly constant touring schedule back in Europe
The following is a comprehensive discography of UFO, an English hard rock band formed in 1969.
 The band became a transitional band between early hard rock and heavy metal and the new wave of British heavy metal.
 UFO's influence was strongly felt in the 1980s heavy metal scene and they have been cited as a primary influence of Steve Harris of Iron Maiden, Kirk Hammett of Metallica, Dave Mustaine of Megadeth, Joey Tempest of Europe, Frank Hannon of Tesla, and Mike McCready of Pearl Jam, among others.
Neoclassical metal is a subgenre of heavy metal that is heavily influenced by classical music and usually features very technical playing, consisting of elements borrowed from both classical and speed metal music.
 Deep Purple's Ritchie Blackmore pioneered the subgenre by merging classical melodies and blues rock.
 Later, Yngwie Malmsteen became one of the most notable musicians in the subgenre, and contributed greatly to the development of the style in the 1980s.
 Other notable players in the genre are Randy Rhoads, Jason Becker, Tony MacAlpine, Vinnie Moore, Uli Jon Roth, Stéphan Forté and Timo Tolkki.
This is a list of avant-garde metal artists, regional scenes, and record labels.
 Avant-garde metal or avant-metal, also known as experimental metal, is a subgenre of heavy metal music loosely defined by use of experimentation and characterized by the use of innovative, avant-garde elements, large-scale experimentation, and the use of non-standard and unconventional sounds, instruments, song structures, playing styles, and vocal techniques.
 It evolved out of progressive rock and various forms of metal, including extreme metal, particularly the extreme subgenre death metal.
 Some early examples are the King Crimson releases "Larks' Tongues in Aspic" and "Red" in 1973 and 1974 respectively, and the 1976 Led Zeppelin album "Presence".
 The genre emerged in the early 1980s through the efforts of bands such as Celtic Frost and Voivod, who pioneered the genre.
 Other pioneers of avant-garde metal include Boris, Earth, Helmet, maudlin of the Well, Neurosis, Sunn O))), and Mr. Bungle.
 In the late 1990s, Misanthropy Records emerged as a promoter of Norwegian avant-garde metal until it folded in 2000, and, according to Jeff Wagner, in the late 1990s and early 2000s, a so-called "new wave of avant-garde metal" was spearheaded by The End Records.
 Some other record labels which promote avant-garde metal are Aurora Borealis, The Flenser, Holy Records, Hydra Head Records, Ipecac Recordings, Napalm Records, the Relapse Entertainment imprint of Relapse Records, Seventh Rule Recordings, and Southern Lord Records.
 In the United States, local avant-garde metal scenes have emerged in the San Francisco Bay Area, with bands such as Giant Squid, Grayceon, and Ludicra, Boston, with bands such as Isis, Kayo Dot, and maudlin of the Well and Seattle.
 According to the "New York Times", some regional scenes that developed in the mid-1990s included the cities of Tokyo, Los Angeles, and Oslo.
Volbeat are a Danish heavy metal band formed in Copenhagen in 2001.
 They play a fusion of rock and roll, heavy metal and rockabilly.
 They are inspired by classic rock and roll artists such as Elvis Presley and Johnny Cash, as well as modern hard rock, thrash metal, heavy metal, alternative rock and hardcore punk groups.
 Their current line-up consists of vocalist and guitarist Michael Poulsen, guitarist Rob Caggiano, drummer Jon Larsen and bassist Kaspar Boye Larsen.
 The band is signed to Dutch label Mascot Records and has released six studio albums and one DVD.
 All of their studio albums have been certified gold in Denmark.
 Their second album "Rock the Rebel/Metal the Devil" received platinum status, and their 2010 release "Beyond Hell/Above Heaven" was subject to widespread international critical acclaim, receiving double platinum in Denmark, platinum in Finland and Germany, and gold in the United States, Sweden and Austria.
 Volbeat's sixth album entitled "Seal the Deal & Let's Boogie" was released worldwide on 3 June 2016.
Venom are an English heavy metal band formed in 1979 in Newcastle upon Tyne.
 Coming to prominence towards the end of the new wave of British heavy metal, Venom's first two albums—"Welcome to Hell" (1981) and "Black Metal" (1982)—are considered a major influence on thrash metal and extreme metal in general.
 Venom's second album proved influential enough that its title was used as the name of an extreme metal subgenre: black metal.

Question: Subgenre of heavy metal, Neoclassical metal, was pioneered by an English rock band formed in Hertford in what year?
Answer: 1968