Helloween is a German power metal band.  The formation has changed a lot but is still considered a pioneer in the genre.

Their second and third album, Keeper of the Seven Keys Part I and Part II are considered like masterpieces.

Helloween just launched their fifteenth album, My God-Given Right, in May 2015.  They'll be on tour and will be stoping in Montreal at the Virgin Mobile Corona Theater in February 2016.