Question: Which vocalist left the band whose fourth full-length album is Destroyer?
Context: Kristian Eivind Espedal (born 7 August 1975), better known by his stage name Gaahl, is a Norwegian vocalist and artist.  He is best known as the former frontman of Norwegian black metal band Gorgoroth.  He is also the founder and frontman of Trelldom and Gaahlskagg.  Since leaving Gorgoroth he has been involved with God Seed, Wardruna, and Gaahls Wyrd.  He was the focus of the documentary "True Norwegian Black Metal" and also appeared in the film "Flukt". In the Unlikely Event is the fourth full-length album by American progressive rock band The Fall of Troy, that was released on October 6, 2009.  The album was recorded with producer Terry Date and is the only full-length album to feature bassist Frank Ene (first featured on "Phantom on the Horizon").  It was recorded at Studio Lithio.  The album featured a slightly less aggressive style compared to the band's earlier work, in turn facing mixed critical reception. The Fourth Legacy is the fourth full-length album by power metal band Kamelot.  It was released in 1999 by Noise Records/Modern Music.  It was the first album to credit vocalist Roy Khan as a writer on all tracks, establishing him as the main songwriter of the band together with founder and guitarist Thomas Youngblood. Destroyer – or About How to Philosophize with the Hammer is the fourth full-length album by Norwegian black metal band Gorgoroth.  It was their first release on Nuclear Blast.  It contained eight tracks performed by several different lineups, with band founder Infernus being the only member to be featured on all tracks.  Four different vocalists were featured on the album, including Infernus on two tracks, Pest on four tracks, and T-Reaper and new vocalist Gaahl each on one track. Summer Bones is the fourth full-length studio album from the American pop punk band Hit the Lights, released on March 24, 2015.  It was produced and mixed by Kyle Black (New Found Glory/Icon For Hire/Forever Came Calling).  This is the band's first release on Pure Noise Records, as well as being their shortest full-length album to date.  The album's final track features guest vocals from original vocalist Colin Ross. Arvas, formerly known as Örth, is a Norwegian black metal band formed in Bergen in 1993 as a one-man project by multi musician V-Rex.  In Summer 1996, Borknagar drummer Grim and Gorgoroth bassist Ares joined the band.  They recorded an album in Winter 1996, titled "Nocturno Inferno", but it was never released.  After Grim committed suicide in 1999, V-Rex decided to keep on going as a one-man project, but changed the band's name.  He recorded two demos, "Countless Souls at Dawn" and "I Am Thy Grief", and a split album with Hordagaard titled "Dawn of Satan/Uncle Satan", which was released by Azermedoth Records.  The band's first official full-length album "Blessed from Below – Ad Sathanas Noctum" was released in 2010 by the band themselves.  Their second album "Into The Realm Of The Occult" was released in November 2013 by Italian label ATMF Records, to be followed in March 2015 by "Black Satanic Mysticism", via Aeternitas Tenebrarum Music Foundation.  Arvas has shared stages with bands like Throne Of Cartasis, Urgehal, Dauden, 1349, Mongo Ninja, Nocturnal Breed.  In March 2013 Arvas toured the east European countries supporting Deicide on their 'End Of The World Tour'.  The band's fourth full-length, "Black Path", was released on 24 March 2017 by Mighty Music. Oh, Sleeper is an American Christian metalcore band from Fort Worth, Texas that forged themselves in 2006 with ex-members of Between The Buried and Me, As Cities Burn, and Terminal.  In over a decade's span, Oh, Sleeper released three full-length albums and two EPs through Solid State Records, and toured worldwide as an opening act.  After independently releasing "The Titan EP" and travelling in the full Van's Warped Tour 2013, the band went on hiatus to allow clean vocalist and lead guitarist Shane Blay to join former-As I Lay Dying members in starting California-based metal band Wovenwar.  The band plans to release their fourth full-length album release, "Bloodied//Unbowed" in 2017. Fireflight is an American Christian rock band formed in Eustis, Florida in 1999.  The band is signed by Flicker Records.  They have played in ShoutFest, Revelation Generation, and have been featured on The Scars Remain tour with Disciple, Family Force 5, and Decyfer Down.  While touring, they wrote their third album, "Unbreakable" (2008), and released their first single off the album, "Unbreakable".  They performed at Winter Jam 2010 and released their fourth full-length album "For Those Who Wait" in February.  On December 1, 2010, they were nominated for their first Grammy award.  In 2012 they came out with their fifth full-length album "Now". The Stryder was a band hailing from Long Island, NY.  The Band was formed by Peter Toh and Scottie Redix in 1999 after their previous project, Yearly, disbanded following the departure of bassist Eben D'amico who left to join Saves the Day.  They added a vocalist and bassist, John Johansen and Nick Wendel (Respectively).  They released a 7" on Elkion Records titled "The Hits Just Keep on Comin" and shortly after signed a deal to Equal Vision Records and released their debut album "Masquerade in the Key of Crime" in the summer 2000.  The band toured extensively and began writing new material in 2001.  They added former Glassjaw drummer Durijah Lang, and moved Scottie Redix up to Guitar and backing vocals.  In the summer of 2001 the band parted ways with vocalist John Johansen.  2002 saw the release of "Jungle City Twitch".  Debuting a new sound, The Stryder continued to tour the country in support of the new release.  In 2003/2004, Elkion Records released "Savor The Danger" which contained a collection of old demos and the 2 songs from the 7" previously released on the label.  Peter released his first solo EP "Cleopatra" in 2004 on Elkion Records.  Durijah moved on to become the drummer of Classic Case and in 2007, became Pete Parada's replacement in Saves The Day.  In 2006, Peter then went on to start an Internet TV/New Media Company, Hidden Track TV with Adam Schleichkorn, and released a solo EP titled "Shoes of a Beast".  Peter is currently working on his first full-length album, titled "Wildlife".  Scottie Redix now plays under the moniker 'Cassonova Brown' and is currently working on his first full-length.  The Working title for the album is"On the Wall" and there are 2demos available on Soundcloud.com.  Scottie is also a member of the musical collective Teachers, who also have a full-length album titled "Anesthesia" slated for an early 2013 release.  Teachers contributed to Kanye West's "Monster". The Maine is an American rock band from Tempe, Arizona, formed in 2007.  Their first release, the EP "Stay Up, Get Down" was released in late 2007, followed by a five-song EP titled "The Way We Talk" on December 11, 2007.  The band's first full-length album, "Can't Stop Won't Stop" was released July 8, 2008. " ...And a Happy New Year" was released in December 2008.  Their second full-length album, "Black & White", (July 13, 2010) sold 22,634 copies in its first week.  On December 6, 2011, the group's third album, "Pioneer", was released and it peaked at No. 90 on the Billboard 200.  Their fourth full-length record "Forever Halloween"(June 4, 2013) reached No. 39 on the Billboard 200 by selling over 10,000 copies in its first week and was followed by its deluxe edition on June 17, 2014.  Their fifth studio album, "American Candy", was released on March 31, 2015. " Lovely Little Lonely", their sixth full-length record, was released on April 7, 2017.
Answer: Kristian Eivind Espedal