There are multiple artists with this name:
1) Merciless is a Swedish death metal/thrash metal band. The band was formed during the summer of 1986 in Strängnäs, Sweden by Erik Wallin (guitar) Fredrik Karlén (bass guitar) and Stefan Carlsson (drums).
They were inspired of the early fast-playing bands such as Kreator, Sodom, Destruction and Bathory.
First they did some local gigs as "Obsessed" and "Black mass" but changed their name to Merciless in early 1987. A demo was recorded titled "Behind the Black Door", which led to the replacement of Kåle by Rogga in early 1988. With this line-up they recorded a second demo "Realm of the Dark" in June 1988. This demo drew the attention of Deathlike Silence Productions - the label of Euronymous. That label released their debut album The Awakening in March 1990. Their second album The Treasures Within was recorded in June and July 1991 but it was not released until a year later due to the mismanagement of their new label Active Records. This delay cause the departure of drummer Stipen who was replaced by Peter Stjärnvind in February 1992. In September of 1993, after Scandinavian tour, they recorded their third album, Unbound, with Dan Swanö at the Unisound studios and was released by No Fashion Records. In 1994 the band broke up because of disillusionment with record labels, but got back together in 1995 to record the song "Cryonics" for the Slayer tribute album. In 1999 their debut album was re-issued by Osmose Productions, which eventually led to the reinstallment of the band. In May 2002, they entered the studio to record the successor to their 1994 album, simply named Merciless.
2) Merciless is a hardcore band from Seattle, Washington
3) Merciless A.k.a. War Head is a DJ from Jamaica. Read more on Last.fm.