Helloween is a German power metal band founded in 1984 in Hamburg, Northern Germany by members of bands Iron Fist and Gentry. Its first line-up consisted of singer and guitarist Kai Hansen, bass guitarist Markus Grosskopf, guitarist Michael Weikath, and drummer Ingo Schwichtenberg. After the release of a self-titled EP and their debut album Walls of Jericho in 1985, it expanded into a quintet with the addition of singer Michael Kiske, Hansen choosing to focus on guitar instead. Under this line-up, they released the Keeper of the Seven Keys albums (1987 and 1988), which established Helloween as a notable heavy metal band and led to the creation of the power metal subgenre. However, Hansen left the band quickly after the release of Part II and was replaced by Roland Grapow. He then created the band Gamma Ray.
Helloween's first two albums without Hansen, Pink Bubbles Go Ape (1991) and Chameleon (1993), were commercial and critical failures, which created tensions between band members and led to the firing of Schwichtenberg and Kiske. They were replaced by Uli Kusch and Andi Deris respectively. The albums released under this line-up, Master of the Rings (1994), The Time of the Oath (1996), Better Than Raw (1998) and The Dark Ride (2000), received warmer reception from both fans and critics, gradually establishing Helloween as a successful band again.
However, tensions led to the dismissals in 2001 of both Grapow and Kusch, who then went on to found Masterplan together. Grapow was replaced by Sascha Gerstner, but the attempts to find a new drummer were chaotic and no band member was credited for drums on the album Rabbit Don't Come Easy (2003). The band finally found a stable drummer in Daniel Löble in 2005. Under this new line-up, the longest in its history, the band has released four successful studio albums: Keeper of the Seven Keys: The Legacy (2005), Gambling with the Devil (2007), 7 Sinners (2010), and Straight Out of Hell (2013), with all members except Löble contributing to songwriting. Their fifteenth studio album, My God-Given Right, was released on 29 May 2015.
On 14 November 2016, the band announced that both Kai Hansen and Michael Kiske were rejoining Helloween for a world tour, titled Pumpkins United World Tour, to conclude in 2018.
Since its inception, Helloween has released fifteen studio albums, three live albums, three EPs, and twenty-seven singles, and has sold more than eight million records worldwide.