The song was immediately popular amongst heavy metal fans in the United Kingdom upon its initial release, but only rose to international prominence after Metallica covered the song as a B-side on their 1984 single "Creeping Death"; the cover was then re-released on their 1998 cover album Garage Inc. The song was influenced by Black Sabbath's 1975 song "Symptom of the Universe". The song starts with an instrumental segment with excerpts of Gustav Holst's The Planets (1914–16).
