Helloween is a German power metal band founded in 1984 in Hamburg by members of bands Iron Fist, Gentry, Second Hell and Powerfool. It is said that the band is one of the most influential European heavy metal bands of the 1980s. Its first lineup consisted of singer and guitarist Kai Hansen, bassist Markus Grosskopf, guitarist Michael Weikath and drummer Ingo Schwichtenberg. By the time Hansen left Helloween in 1989 to form Gamma Ray, the band had evolved into a five-piece, with Michael Kiske taking over as lead vocalist. Schwichtenberg and Kiske both parted ways with Helloween in 1993; Schwichtenberg died two years later as the result of suicide. Between then and 2016, there had been numerous line-up changes, leaving Grosskopf and Weikath as the only remaining original members. As a septet, their current lineup includes four-fifths of the Keeper of the Seven Keys: Parts I and II-era (1987–1988) lineup, featuring three additional members, vocalist Andi Deris, guitarist Sascha Gerstner and drummer Daniel Löble.

Power metal is a subgenre of heavy metal combining characteristics of traditional heavy metal with speed metal, often within a symphonic context. Generally, power metal is characterized by a faster, lighter, and more uplifting sound, in contrast with the heaviness and dissonance prevalent in, for example, extreme metal. Power metal bands usually have anthem-like songs with fantasy-based subject matter and strong choruses, thus creating a theatrical, dramatic and emotionally "powerful" sound.