A lot of the time, the hate mail Bob Lefsetz receives is simple and succinct, stuff like “You are a fucking shithead” or “You are an amazing douche.” But once in a while, the put-downs get more elaborate, as was the case when Kid Rock lashed out at Lefsetz in a 2007 email. “Your a failed musician with a big mouth,” wrote the rapper-singer, his typing fingers undoubtedly damaged by years of devil-horn gesticulations. “You do NOTHING but talk. See you on the streets you punk ass mother fucker!!”

Lefsetz is the author of the Lefsetz Letter, an online record-biz op-ed that mixes analysis, rants, boomer-rock reveries, and the odd bit of futurism. Like most music bloggers, Lefsetz posts frequently and verbosely; unlike most music bloggers, he has actually gained the interest of the music industry, so much so that even Lefsetz’s most casually tossed-off missives get noticed. The line that irked Rock: A simple “Fuck Kid Rock”—just the sort of low-grade blogenspiel that a star of Rock’s stature would normally shrug off.

But Rock was compelled to respond, as are many of the musicians, managers, and producers Lefsetz calls out (or, on occasion, praises effusively) in his Letter. It’s tough for them to ignore his latest proclamation, because even if they try, they’ll probably just wind up hearing about it from somebody else. “At every label,” says Scott Rodger, manager for Paul McCartney and Arcade Fire, “from the mail room to the A&R department to the chairman’s office, I guarantee they all read him.”

Which is strange, given that many of Lefsetz’s readers would have a hard time naming a single achievement from his pre-Letter career. Though one of his online bios refers to him as an “industry legend,” Lefsetz, 58, was actually fired from his midlevel record-biz gig two decades ago. A former lawyer, he has never produced a Top 40 song or signed a hit band, and unlike other members of the web’s pop-culture commentariat—Nikki Finke, Harry Knowles, the solemn-honky cabal at Pitchfork—Lefsetz doesn’t get scoops or launch careers.

Instead, he sits in the Santa Monica, California, apartment he shares with his girlfriend and writes lengthy, sporadically caps-locked screeds about everything from overpaid executives to kowtowing artists. He’s become a sort of digital-era pamphleteer, working alone at all hours of the night, nailing manifestos to the church door—manifestos that call for revolt, for sanity, and for a deeper appreciation of Jackson Browne. And, in an industry whose few survivors still strive for a certain on-the-record chumminess, Lefsetz always names names. “Bob’s not beholden to anybody,” says music manager (and longtime friend) Jake Gold. “So he can afford to say whatever’s on his mind.”

That’s why, in addition to containing the occasional threat of bodily harm, Lefsetz’s inbox also surges with fan mail. There might be a note of support from Quincy Jones or an invitation to dine with a major-label head. Even Kid Rock came around, and the two are now occasional email buddies. Lefsetz’s followers are a lot like him: music-biz lifers who’ve watched the record industry become downgraded from a pop culture superpower to a desperate banana republic. And, like him, they miss the glory days.

Lefsetz won’t reveal the size of his audience, except to say that it’s “much, much bigger” than hundreds of thousands. He now makes a living the same way many artists do: by giving away his work for free online and then hitting the road—in his case as a paid speaker at music conferences.

Still, for all of Lefsetz’s ever-increasing visibility, he remains a bit of a mystery. During a 2009 Canadian music conference, after Lefsetz blasted Kiss frontman Gene Simmons for his keynote speech, the two had a public showdown. It was an awkward exchange, and halfway through, the towering, gargoylish Simmons turned to the impishly belligerent Lefsetz and posited a question many in the industry have been wondering for years: “Who the fuck are you?”

As readers of his letter can attest, Lefsetz occasionally indulges in broad, far-reaching analogies that don’t so much digress as loop through some distant metaphorical cosmos, stopping off at several far-off planets along the way. Over brunch in Beverly Hills, he lays out one prime example, which we’ll call the Aniston Axiom.

“Let’s say you’re a unionized worker on the line,” Lefsetz says. “You’re working some overtime, you’re making some pay. You have a house, and you have a boat, and you’re sitting there having sexual fantasies about somebody on Friends . You say, ‘If I moved to Hollywood, I could fuck Jennifer Aniston.’ And you truly believe it. To get from there to actually fucking Jennifer Aniston is not impossible, but it’s an unbelievably long journey.”

We’re at a corner table on the patio of a restaurant at the Four Seasons, where Lefsetz occasionally meets with record-biz pals. He’s dressed like a dad touring a college campus on parents’ weekend: jeans, sneakers, long-sleeve polo with the collar popped. Lefsetz’s resemblance to Wallace Shawn (Vizzini in The Princess Bride , himself in My Dinner With Andre ) has been invoked before, and while it’s an apt comparison, what’s most jarring is how, at moments of heightened emphasis, he also conjures the actor’s pinched voice (“Inconceivable!”).

The point of the Aniston story, which goes on for a while, is that while millions of people dream of making it in the music business, only a few have the talent and hubris to actually do so. It’s an obvious observation, perhaps, but one Lefsetz says is lost on the countless musicians who email him every day, looking for a shortcut to fame. “The wannabes,” Lefsetz says, using one of his favorite put-downs, “have no idea how sophisticated the game is.”

Target Gene Simmons Attack At a conference in 2009, Lefsetz accuses Simmons of shamelessly promoting his new label. “When does Gene Simmons give back,” Lefsetz asks, “as opposed to only being about what’s in his fuckin’ wallet?” Counterattack Simmons assails Lefsetz’s credibility: “What have you done?” he asks. “What’s your qualification for even farting through your oral passage?” Target Taylor Swift Attack After Swift’s off-key Grammy performance in January 2010, Lefsetz—an early supporter of the country star—writes, “Taylor Swift can’t sing,” and that she “shortened her career last night.” Counterattack The 2010 Swift song “Mean” is rumored to have been written about Lefsetz. Target Kid Rock Attack Writing about the Country Music Awards in 2007, Lefsetz dismisses the rapper-singer with a terse “Fuck Kid Rock.” Counterattack In an email, Rock writes: “You can mother f—me all day long, but i will see you one day, and when i do it will be fun to watch you bitch up!” The two men have since made up. Target Irving Azoff Chairman, Live Nation Attack In April 2011, Lefsetz assails the seven-figure salaries of several Live Nation executives, calling the company’s recent performance an “utter disaster.” Counterattack Azoff, a longtime friend of Lefsetz, disputes the figures. (“I wanted him to do his fucking research,” Azoff tells Wired .) After a frosty period, the two appear to have reached a détente.

Illustration: Boneface

Lefsetz has lived in LA since the ’70s, when he moved here to follow his dream—his Aniston, if you will—of getting into the music industry. He was raised in the suburbs of Connecticut and went to college in Vermont, and his writing often draws on the musical experiences he had in those formative years: His first listen of “I Want to Hold Your Hand” on a car radio; his devotion to Neil Young’s “Down by the River,” which he learned to play on guitar.

Back then, music functioned as a sort of social shorthand. Lefsetz could walk into a party and start discussing the latest single, and everyone would know what he was talking about. “In the ’60s and ’70s, music drove the culture,” he says. “It was the best way to connect to your generation.”

He’d hoped to be a music journalist, but when a college teacher criticized his writing, a dejected Lefsetz started looking for an alternate route to the music business. By the early ’70s, the record industry was becoming increasingly corporate, and lawyers were suddenly in demand, so he enrolled in law school. After earning his degree, he moved to LA, where he was soon handling contracts and negotiations.

Eventually, Lefsetz wound up at a management company called Sanctuary, serving as a creative consigliere to heavy-metal acts like W.A.S.P. and doing office work for other heavy-metal acts like Iron Maiden. But after he clashed with W.A.S.P. frontman Blackie Lawless—Lefsetz says they couldn’t agree what song to release as a single—he was fired. A few ancillary gigs followed, including work on some low-budget movies. Then in 1986, while perusing Billboard , Lefsetz felt a renewed urge to write. “I thought, ‘I could do better than this,'” he says. What was missing, he felt, was analysis. “There were facts and figures, with questionable accuracy, but no one making sense of them all.”

It was the dawn of the desktop publishing age. Lefsetz taught himself to use a computer and started the Lefsetz Letter, a six- to eight-page printed bulletin full of tips and commentaries. (Sample talking point from this era: Is Steve Winwood sacrificing his credibility by dancing in his music videos?) He bought a showbiz directory and mailed copies to label execs, hoping to get their attention. “They didn’t know who the fuck I was,” he says. “My goal was to get another job in the music business, not to be the guy writing the newsletter.”

Over time, though, he realized he could use the Letter to speak to an industry that was experiencing a fresh epoch every few years: the hostile takeover of radio by MTV, the outbreak of indie labels and hip hop, the ignoble demise of hair metal. Lefsetz believed that, from the outside, he could help those on the inside understand what was happening.

By the late ’80s, the Letter had become popular enough that Lefsetz could make a living at it, at one point charging more than $100 for a yearly subscription. Then, in 2000, he dropped the fee and put the Letter online. (He has never taken advertising and instead has earned money from syndication deals, speeches, and occasional consulting gigs.) The timing for Lefsetz’s digital debut couldn’t have been better: Mainstream music mags were more interested in artist profiles than industry gossip, blogs barely existed, and “pop-culture pundit” had yet to become a widely held vocation.

Even better for Lefsetz, Napster was just getting started. If any single issue has helped accelerate Lefsetz’s career and burnish his cred, it’s the war over online music. Lefsetz spent the early ’00s haranguing the labels for trying to shut down Napster, arguing that file-sharing was not only an inevitability but a necessity. In retrospect, this stance may not seem especially shocking. But within the record industry, it was utterly seditious. “I got a certain amount of heat from the usual suspects, i.e., the label people,” Lefsetz says. “But the tide was turning, and people needed someone to explain the new world to them.”

By taking up Napster’s cause so fervently, Lefsetz not only earned himself a reputation as a quasi futurist, he also lucked into an irresistible—and renewable—narrative, one that frequently casts the label heads (and sometimes the artists) as the villains and the music lovers as the victims.

It’s an ideological tactic Lefsetz has employed ever since, whether it means assailing artists for high ticket prices or bemoaning the endless procession of roboto-perfecto pop singers. These are, for Lefsetz, highly personal causes; he has devoted so much of his life to music—it’s both his love and his livelihood—that the industry’s missteps feel like betrayals. And he’s not alone. Lefsetz’s columns tap into a populist rage that resonates with several species of music lovers all at once: the indie-minded purists who think the major-label game is rigged, the technocrats who want music digitally available to everyone, and the aging listeners who can’t understand why anybody would rather listen to Ke$ha than Derek and the Dominos.

Lefsetz’s truths—that the labels blew it with Napster, that artists are better off on their own—are not all that radical. But consider the powers to which they speak. The music industry has long been resistant to change, and even today there’s the sense that a few stubborn lifers are still trying to put on a united-denial front: We’re gonna be fine, really! All we need is for everyone to stop pirating music. Oh, and for Michael Jackson to be alive again, and then to die again. In the meantime, would you like to buy this new Christina Aguilera/will.i.am single? It’s called “Pork Product,” and it sounds like Ethel Merman deflowering a Commodore 64.

To those still hoping for a last-minute return to the industry’s heyday, the Letter is an oft-unwelcome reality check. “You get two groups of people pissed at you,” Lefsetz says. “The people running the old game, and the people who want to be the last ones to get in on the old game. They say, ‘Hey, don’t write about the major labels, because I want to get signed. I wanna get paid.'”

Lefsetz is a digital-era pamphleteer, posting manifestos that call for revolt, for sanity, and for a deeper appreciation of Jackson Browne.

Lefsetz has in fact jeopardized friendships because of the Letter. He got into a tiff with Live Nation chair and Eagles manager Irving Azoff last year when he reprinted (and criticized) the company’s executive salaries. The two have since made up, in part because Azoff—who praises Lefsetz’s “incredible passion”—has known him since the ’80s and is used to such tiffs. “I have a senior executive who calls him an ‘equal-opportunity fucker,'” Azoff says, laughing. “He fucks everybody equally.”

Other victims have been less forgiving. In 2007 Lefsetz wrote a gushing ode to Taylor Swift, who at the time was a star only in country-music circles. (“Melody and hooks are not dead,” he wrote, “nor is authenticity.”) Swift got in touch with Lefsetz, occasionally emailing or calling him. But after he wrote a takedown of Swift’s performance at the Grammys in 2010, he says, the correspondence stopped. A year later, rumors started circulating that Swift’s song “Mean” was a thinly veiled attack on Lefsetz.

The tune is about an unnamed antagonist who’s “washed up and ranting about the same old bitter things,” and in the album liner notes, Swift’s highlighted letters spell out the message “I thought you got me.” (Lefsetz says she told him “You get me” several times; Swift did not respond to requests for comment.)

It’s not hard to see why Swift would have been upset by Lefsetz’s reversal. He dismisses her, saying, “Now everyone knows she can’t sing,” and adding that “in one fell swoop she’s consigned herself to the dustbin of teen phenoms.” Lefsetz has included lots of details about his life in the Letter—things like his divorce in the ’90s and his recent health problems (in 2009, Lefsetz was diagnosed with CML, a treatable form of leukemia: “I have the one and only cancer there’s a pill for,” he says). But as intimate as his writing can get, the Swift attack was one of the most personal tracts Lefsetz had ever written. You got the sense that he felt duped, that he really believed in her. Which, for Lefsetz, doesn’t happen a whole lot anymore.

Toward the end of our brunch, Lefsetz and I start talking about new music. Though he’s enthused in the Letter about a few emerging acts—including roots-rock groups like Mumford & Sons and electronic artists like Deadmau5—he can’t find a lot to recommend as of late, in part because he holds artists to exacting, impossible-to-satisfy standards. Why listen to the White Stripes or Arcade Fire, Lefsetz argues, when you can listen to Led Zeppelin?

As a result, debating music with Lefsetz can be frustrating—like talking film with someone who compares everything to 2001. And, indeed, if you scan the various Lefsetz-skewering tirades that occasionally pop up on music blogs, you’ll find this is what drives his detractors crazy: For all his talk of the future, Lefsetz would prefer to live in the past, ideally a past where he’s lounging in a ski chalet somewhere listening to James Taylor bootlegs.

That may be true, but what’s also true is in Lefsetz’s perfect world, you’d be there with him, listening to those same records. Despite his constant pressing for change, he still pines for a time when music was mass, in every sense of the word—when everybody at the party knew the tune.

A few years ago, Lefsetz wrote that some of the strongest relationships of his life have been with music. “Maybe it’s just that connecting with other human beings is not my forte,” he wrote. “They’re subtle, they’re moody, they get distracted. Unlike records. Which are static, frozen in time.”

At one point, I mention to Lefsetz that I don’t necessarily think the end of a monoculture is a bad thing—that I’m perfectly fine in my own self-curated pop-cultural microcosm. “But you have a world that works,” Lefsetz says. “You have a wife and a kid, et cetera. For those of us who don’t, where music is going is a primary concern.”

Lefsetz isn’t exactly a lonely guy. He has a steady girlfriend, gets taken out to nice meals, and can get on whatever guest list he wants. But in a real way, it’s still those frozen-in-time records that keep him tethered to this world. This is partially why he remains desperate to understand music’s future, whatever that may be. Because it’s his future too.

Contributing editor Brian Raftery (@BrianRaftery) profiled director David Fincher in issue 19.12.