For Metallica, Lulu was a chance to try something new – to wing it with a rock hero. For Lou Reed, however, it was different. In fact, Reed once described the album – which arrived on Nov. 1, 2011, amid a shower of negative critical responses – as "this idea I’ve had almost forever."

All he was missing, Reed told The New York Times in 2011, were the right collaborators, something he finally found with Metallica. "It needed a very, very powerful backing so that it would make sense – and there they were, right off the bat," Reed noted. "That made it possible for me to do this. And then when we really went at it, the sky opened.”

Lulu, which the paper memorably described as "a set of wrenching, astonishingly profane songs inspired by two century-old German plays," combined work inspired by Spring Awakening author Frank Wedekind with a vicious, if occasionally repetitive, thrash beat. That led to some level of confusion among both fan bases, as USA Today noted that Lulu "raised eyebrows, then hackles."

Perhaps it was simply too loud for Reed's most erudite fans. Maybe Lulu, with its admittedly convoluted tale of a serial femme fatale killed by Jack the Ripper, was a touch too literary for Metallica's head-banging followers. Maybe the combination just hadn't worked. After all, Pitchfork found the concept "audacious" but the results "exhaustingly tedious" – and they weren't alone in that opinion. The Village Voice said the project "could charitably be described as 'unpleasant.'"

Reed, who died in 2013, stood firm in the face of ferocious criticism. "They are my metal blood brothers," Reed said of Metallica in a talk with USA Today. "They're very brave, and they can play. I'm not easy to play with. Some of [Lulu] that sounds easy is actually really hard. A lot of cool players can't do that. Academia drove it out of them."

Reed had long pushed against rock convention, leveraging noise as a new form of musical aggression all the way back to his days in the Velvet Underground. And anyone who has really listened to "Venus in Furs," "Walk on the Wild Side" or 1973's Berlin knows quite well Reed's interest in exploring sexual deviance, moral frailty and lingering desire. Metallica may have become something of a mainstream band along the way – their previous two albums had sold nearly four million copies, while Reed couldn't move 70,000 – but they began life as outsiders too.

That's why, even if Lulu didn't necessarily click with every listener, it remained a special experience for those involved. “We’ve always hovered in our own autonomous little bubble," drummer Lars Ulrich told the The New York Times, "and if you look at Lou’s career, he’s always been on the periphery, on the fringes.”

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Their relationship dated back to 2009, when Reed joined Metallica at Madison Square Garden for a Rock and Roll Hall of Fame concert. An enthused Reed at first proposed recording some of his earlier unfinished material, before changing his mind – just two weeks before the sessions were to begin.

Instead, he suggested songs he had originally composed for a theatrical production by director Robert Wilson but had never quite given up on. Reed emailed the rough Lulu sketches to Metallica, who wrote new arrangements. Then Reed and producer Hall Willner joined them at the band's San Rafael, Calif., studio.

"It was so deep," Ulrich told USA Today. "I called Lou and said, 'I don't know where this is going, but we're in.'" The project then began to move at lightning speed. “Within the week that they were supposed to be investigating the place, we had more than half the album recorded,” guitarist James Hetfield told The New York Times. “We just went out and started jamming.”

Lulu wasn't without its fans – beginning with Reed himself, who was never one to mince words when it came to detractors. “Who cares?” he snapped in a 2011 talk with the Telegraph. “I never wrote for them then, I don’t write for them now. I have no interest in what they have to say about anything. I’m interested in whether I like it. I write for me.”

Ulrich compared it to the moment when their own fans became apoplectic over the appearance of acoustic guitars on "Fade to Black" from 1984's Ride the Lighting. "There was a nuclear meltdown in the heavy metal community; there have been many more since then," he told USA Today. "This is something they've never heard. Nobody hears rhythms or delivers poetry the way Lou does. It's not for everyone, but I think it's a fantastic record."

David Bowie offered unabashed praise too. "Listen, this is Lou’s greatest work," he told wife Laurie Anderson, who relayed the story at Reed's Hall of Fame induction. "This is his masterpiece. Just wait, it will be like Berlin. It will take everyone a while to catch up."

Whatever its legacy, Lulu helped Reed complete a long-delayed creative dream – critics be damned. "We pushed as far as we possibly could within the realms of reality," Reed told the Guardian. "This is the best thing I ever did, and I did it with the best group I could possibly find."

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