The group's ascent marks a mysterious rarity: despite three full-length albums and two EPs to its name, Ghost's official members remain essentially anonymous, with its frontman an undead Pope-like figure referred to as Papa Emeritus (I through III; the frontman is "replaced" with each album) and the remainder considered Nameless Ghouls.
"Hammer" is from Ghost's Popestar EP (released in September), featuring the original song alongside covers of Echo & the Bunnymen, Eurythmics and more. The set debuted at No. 1 on the Top Rock Albums and Hard Rock Albums charts with 21,000 sold in its first week, according to Nielsen Music.
"Hammer" is also the first Mainstream Rock Songs No. 1, dating to the chart's 1981 launch, for an act from Sweden -- a country known more for its pop exports like ABBA, Roxette and mastermind songwriter-producer Max Martin.
Still, Northern Europe has forged its triumphs on Mainstream Rock Songs, most recently with Denmark's Volbeat, whose "The Devil's Bleeding Crown" spent nine weeks at No. 1 last year. Other foreign acts to lead the list in recent years hail from the United Kingdom (Bring Me the Horizon, Royal Blood) and Canada (Three Days Grace, Nickelback).