Question: What was the former name of the Swedish band formed in 1989 with a music style that employs highly melodic guitar riffs, often borrowed from traditional heavy metal?

Context paragraphs:
Mortem: Mortem is a death metal band formed in 1986 in Lima, Peru.  They are the first Peruvian metal band to have toured Europe and the United States.  Mortem’s musical style is firmly rooted in the death metal, black metal and thrash metal of the nineteen-eighties.  Mortem's characteristic heavy sound is defined through slow and sinister death metal alternated with fast and aggressive counterparts.  Frantic tremolo picking in the style of early Possessed and Death built on passionate rhythmic percussion topped with wailing atonal and melodic guitar solos comprise a potent mix which lives up to the principle of death metal technique to craft pounding ritualistic and spirited death metal.  Vocals are forged from guttural rasps and often develop into high shrieks while lyrics deal mainly with the occult and anti-Christianity.

Thrash metal: Thrash metal is an extreme subgenre of heavy metal music characterized by its fast tempo and overall aggression.  The songs usually use fast percussive beats and low-register guitar riffs, overlaid with shredding-style lead work.  The lyrics often deal with social issues and reproach for The Establishment, using direct and denunciatory language, an approach borrowed from hardcore punk.

Alternative metal: Alternative metal (also known as alt-metal) is a rock music fusion genre that infuses heavy metal with influences from alternative rock and other genres not normally associated with metal.  Alternative metal bands are often characterized by heavily downtuned, mid-paced guitar riffs, a mixture of accessible melodic vocals and harsh vocals and sometimes unconventional sounds within other heavy metal styles.  The term has been in use since the 1980s, although it came into prominence in the 1990s.

Darkthrone: Darkthrone is a Norwegian heavy metal band.  It formed in 1986 as a death metal band under the name Black Death.  In 1991, the band embraced a black metal style influenced by Bathory and Celtic Frost and became one of the leading bands in the Norwegian black metal scene.  Their first three black metal albums—"A Blaze in the Northern Sky", "Under a Funeral Moon" and "Transilvanian Hunger" (sometimes dubbed the "Unholy Trinity") — are considered the peak of the band's career and to be among the most influential albums in the genre.  For most of this time, Darkthrone has been a duo of Nocturno Culto and Fenriz, who have sought to remain outside the music mainstream.  Since 2006, their work has strayed from the traditional black metal style and incorporated more elements of traditional heavy metal, speed metal and punk rock, being likened to Motörhead.

Nu metal: Nu metal (also known as nü-metal and aggro-metal ) is a form of alternative metal that combines elements of heavy metal music with elements of other music genres such as hip hop, alternative rock, funk and grunge.  Nu metal bands have drawn elements and influences from a variety of musical styles, including multiple genres of heavy metal.  Nu metal rarely features guitar solos; the genre is heavily syncopated and based on guitar riffs.  Many nu metal guitarists use seven-string guitars that are down-tuned to play a heavier sound.  DJs are occasionally featured in nu metal to provide instrumentation such as sampling, turntable scratching and electronic backgrounds.  Vocal styles in nu metal include singing, rapping, screaming and growling.  Nu metal is one of the key genres of the new wave of American heavy metal.

List of melodic death metal bands: This is a list of melodic death metal bands.  Melodic death metal is a heavy metal music style that combines elements from the new wave of British heavy metal (NWOBHM) with elements of death metal.  The term Gothenburg metal is often used to describe bands associated with or stylistically similar to the melodic death metal scene that originated around Gothenburg, Sweden.

Busby Marou: Busby Marou (pronounced Buz-bee Ma-roo) are an Australian duo originally from Rockhampton, Queensland.  The duo are characterised by their melodic guitar riffs and meaningful lyrics.  The band primarily consists of Thomas Busby and Jeremy Marou, however several other musicians perform with the duo in concert.  At the APRA Music Awards of 2012, the duo won "Blues & Roots Work of the Year" category.

Dark Tranquillity discography: The following is the discography of Dark Tranquillity a six-piece Swedish Melodic death metal band which was formed in Gothenburg in 1989 as Septic Broiler.  They are one of the longest-standing bands from the original Gothenburg metal scene.  As of 2013, their formation consists of vocalist Mikael Stanne, guitarists Martin Henriksson and Niklas Sundin, keyboardist Martin Brändström and drummer Anders Jivarp.

Melodic death metal: Melodic death metal (also referred to as melodeath) is a subgenre of death metal that employs highly melodic guitar riffs, often borrowing from traditional heavy metal.  The style originated and developed in Sweden (pioneered by At the Gates, Dark Tranquillity and In Flames) and the United Kingdom (pioneered by Carcass) during the early and mid-1990s.  The Swedish death metal scene did much to popularise the style, soon centring in the "Gothenburg metal" scene.

Ceremonial Oath: Ceremonial Oath is a Swedish extreme metal band who formed in 1989 under the name "Desecrator", changed their name to Ceremonial Oath in 1991 and disbanded in 1995.  During their short career they released three demos, one EP and two full-length albums.  Their influence is greater than their short lifespan suggests: several of the band members would later create or join metal bands that would gain fame and fortune on the future metal scene, such as In Flames, an influential band to the melodic death metal genre; and Hammerfall, a band who would greatly influence the awakened interest in power metal and traditional heavy metal.

Supporting paragraphs: Dark Tranquillity discography Melodic death metal
Answer: Septic Broiler