Mercyful Fate is a Danish heavy metal band from Copenhagen, formed in 1981 by vocalist King Diamond and guitarist Hank Shermann. Influenced by progressive rock and hard rock, and with lyrics dealing with LaVeyan Satanism (often with ironic or sardonic use of Christian themes) and the occult, Mercyful Fate was part of the first wave of black metal in the early to mid-1980s, along with Venom and Bathory. The band is also cited as a formative influence on many then-up-and-coming subgenres of heavy metal, including thrash metal and death metal, as well as the Norwegian black metal scene.

Since its inception in 1981, Mercyful Fate has released seven studio albums, two extended plays, and four compilations. After several line-up changes and self-made demos, they released their self-titled EP in 1982, with the line-up of King Diamond (vocals), Hank Shermann (lead and rhythm guitars), Michael Denner (rhythm and lead guitars), Timi Hansen (bass) and Kim Ruzz (drums). With this line-up, the group recorded their first two studio albums: 1983's Melissa and 1984's Don't Break the Oath. In spite of their reputation as one of the most acclaimed bands of the European heavy metal scene of the 1980s, Mercyful Fate were the subject of controversy due to their satanic imagery, and one of their songs "Into the Coven" (from Melissa) later gained notoriety for appearing as one of the PMRC's "Filthy Fifteen" list of objectionable songs.

After disbanding in 1985 due to musical differences, four out of the five members of Mercyful Fate reunited in 1992 and recorded the album In the Shadows, which was released the following year. During the 1990s, the band released four more studio albums and went through several line-up changes. Mercyful Fate went on hiatus in 1999, but had reunited on occasion during the 2000s. On August 1, 2019, it was announced that Mercyful Fate were reuniting on a more permanent basis, with plans to tour and release a new album, which will be their first since 9 in 1999.