The release of Nirvana's paradigm-shifting Nevermind in the fall of 1991 put every popular '80s band on notice. But Iron Maiden had other things on their minds – starting with the release of their ninth album, Fear of the Dark.

Two years earlier, the world-conquering quintet led by bassist and chief songwriter Steve Harris, had weathered its first adversity in almost a decade, when longtime guitarist Adrian Smith -- worn out from so many years of grueling work and dissatisfied with Harris' back-to-basics directive for 1990's No Prayer for the Dying LP -- left the group.

Even though Smith was quickly replaced by fellow New Wave of British Heavy Metal veteran Janick Gers, the new album's lukewarm reception by many critics and fans sent a couple of clear messages that reverberated throughout the Iron Maiden camp: Even the most bulletproof musical career was just one bad album away from ruin, and stagnation was an enemy and they had better evolve or perish.

As a result, Fear of the Dark emerged as one of Iron Maiden's most eclectic albums, melding the surefire familiarity of metallic anthems like rampaging opener "Be Quick or Be Dead" and the epic title track, which bookended a dozen tracks that ranged in style from the ready-made audience singalong of "From Here to Eternity" and the intricate time changes of "Fear Is the Key" to the power ballad "Wasting Love."

But the most radical change had to do with a concerted shift of lyrical focus -- away from the fantasy/history themes of the band's past and toward real-life subjects like the Gulf War ("Afraid to Shoot Strangers"), AIDS ("Fear Is the Key") and football hooligans ("Weekend Warrior").

Even with its relatively experimental nature, Fear of the Dark sounds like a quintessential Iron Maiden album, and a significant improvement over its surprise-challenged predecessor. It shot straight to No. 1 in the U.K., the band's third album to reach that spot. But in the U.S., the band's peak years were looked beyond revival. Still, that didn't stop them from embarking on a record-breaking world tour, where they played to ecstatic sold-out audiences across the globe.

The tour eventually wound down on something of a downer note, after singer Bruce Dickinson announced his departure to resume a solo career -- a move that sent Iron Maiden into a new era of career-threatening challenges. But the turn of events mark Fear of the Dark as a fondly remembered close to one of era of the metal legends' long, eventful story.

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