Daniel Johnston probably won’t be invited to open for Mandy Moore anytime soon, nor would the pouty songbird likely get much applause from the bipolar troubadour’s hipster demographic. But both these performers currently star in movies about the pursuit of fame and the dangerous power of the stories by which we define ourselves to the rest of the world.

Moore appears in American Dreamz, a light-hearted Hollywood farce that finds the foibles of Simon Cowell, George W. Bush, and Osama bin Laden equally amusing. Moore, with her efficiently erotic voice and slutty-girl-next-door looks, is a natural as a small-town barmaid who will let nothing stand in the way of winning an American Idol—style talent contest

Daniel Johnston comes from a darker aisle of the cultural supermarket. His lovely, off-kilter songs and his disturbingly raw performances have made him an alt-music cult figure since he first thrust himself into the Austin, TX, music scene in the 1980s. Fat and unkempt, he plays the leading role not in a Hollywood showcase but an indie documentary, The Devil and Daniel Johnston, which explores his checkered career as a visual and musical artist and occasionally homocidal mental patient.

As you might expect from writer-director Paul Weitz, whose previous handiwork includes American Pie and In Good Company, American Dreamz is more gentle than savage as it pokes fun at a variety of monomanias: George W. Bush’s unshakable resolve, fundamentalist fanaticism, show-biz blonde ambition. President Staton (Dennis Quaid, playing Bush as Forrest Gump’s stupider brother) is beset with self-doubt and retreats to his bed, indulging a sudden yen for newspapers and history books. (This is probably the most sympathetic portrayal of the current president that Hollywood will ever produce.) His chief of staff (Willem Dafoe), a fearsome figure combining Dick Cheney’s hairdo, Karl Rove’s amorality, and the actor’s own cowcatcher teeth, proposes to boost the president’s sagging poll numbers by arranging for him serve as guest judge on the nation’s most popular TV show, American Dreamz.

Its host is Martin Tweed (Hugh Grant, looking scarily dissipated), a no-talent who loathes himself almost as much as he despises the contestants who grovel for his favor. Their lust for celebrity is epitomized by Sally Kendoo (the radiantly peroxided Mandy Moore), whose ruthless pursuit of victory makes Tweed look like a dewy idealist.

Bored with “white trash” like Sally, Tweed commands his sycophantic producers (the delightful Judy Greer and John Cho) to add an Arab contender to the lineup. Their choice is Omer (Sam Golzari), a lover of show tunes who also happens to be a member of an Al Qaeda sleeper cell.

Complications ensue, and there’s a dark undertone to all the joshing—some of it a bit flat, some surprisingly funny—about diva wannabes and posturing politicos. While American Dreamz is too good-natured to score serious political points, its real target is the danger of believing in anything.

That every character wants a piece of the fame pie is taken for granted. So is the idea that the only way to win the world’s attention, or even the notice of your immediate circle, is to mold your identity around some easily graspable story line. In this universe, branding is the central task not only of marketing, but of human existence.

But the gods in American Dreamz smile on those who, like Sally and the president, know the face they present to the world is a fraud; it’s the idealists and ideologues enmeshed in their own hype who are doomed. In a world where conviction has turned deadly, we cheer when cynicism triumphs over belief.

The Devil and Daniel Johnston, by contrast, is all about sincerity. Director Jeff Feuerzeig’s heartfelt tribute to Johnston is as enamored with authenticity as American Dreamz is with slickness.

In its outlines Johnston’s story has the familiar arc of a Behind the Music episode: early promise, fame, disaster, redemption. But like his music, Johnston’s life story takes a familiar pop formula and skews it. His teenage work—elaborate cartoons and short comic films—displayed abundant talent but also insistent, one could say manic, childishness. And what renown he has achieved has always been as much about his freakishness as his artistry.

His first claim to fame was his music, which he recorded on a small tape deck, singing in a little-boy voice ragged with yearning and backed by a crude electric organ. His mode is the love song, but both tunes and words continually veer away from the trite in ways that are simultaneously creepy and poignant. “You must be wrong,” he warbles to an unrequited love, “if you think you don’t love me.”

A series of misadventures landed the 20-something Johnston in Austin, TX, which in the 1980s was an alternative-music epicenter. Johnston pushed his handmade tapes into the hands of critics, musicians, and whoever else would listen, and elbowed his way onto an MTV special about the Austin music scene. “It’s really happened,” he gushes into the camera. “I really am on MTV.”

Even as Johnston became a cult favorite—Kurt Cobain and Matt Groening are among his many famous fans, and his songs have been covered by Yo La Tengo, Tom Waits, and numerous others—his mental health unraveled. Convinced he was locked in battle with demons, he acted out violently against others and himself. Eventually his Austin friends shipped him back to his parents, and for much of the 1990s Johnston shuttled in and out of various mental hospitals.

To tell this story, Feuerzeig draws on hundreds of hours of Johnston’s taped diaries and letters, as well as interviews with his family and friends and footage of Johnston’s performances. The use of old film, crazed with age spots, Johnston’s self-consciously weird drawings, and Feuerzeig’s own offbeat visuals (a huge heart made out of Johnston’s tapes, a monumental shot of a soda machine as Johnston proclaims his love for Mountain Dew) gives the production an outsider feel that jibes well with Johnston’s fantasies of overtaking the Beatles and boxing with Satan.

In addition to its visual intelligence, The Devil and Daniel Johnston is smart in the way it unpacks the moral ambiguities of the “crazy artist” trope. As one of Johnston’s Austin friends, newspaper editor Louis Black, admits, it’s one thing to respect the divine madness of art, quite another to deal with an out-of-control manic-depressive. “I’d always had contempt for people who didn’t understand genius,” Black says ruefully, describing one of Johnston’s suicide attempts. “But what do I do? I say, ‘Put him in the hospital.’”

Feuerzeig shows that Johnston was always aware his mental problems were a means to the notoriety he craved. He stopped taking his medication before performances “because he knew the crazier he was, the better the performance was,” Black says. Early on we hear Johnston’s mother, on one of his tapes, complain, “You’re so hard up for attention and you act insane to get attention!” Johnston also seems to have retreated into madness whenever things were going too well, sacrificing his real life to feed his legend.

To his admirers, Johnston is authentic, so authentic it nearly kills him. Yet Feuerzeig’s portrait is complex enough to show another truth: that mental illness is also Johnston’s brand, the best gimmick he could come up with. If he appeared on American Dreamz—and is there any doubt he’d want to?—he’d be “the wackjob.”

Today, bloated, medicated, and apparently stabilized, he lives in his parents’ basement and continues to make music and draw. He’s developed a thriving second career as an outsider artist of sorts, while performing occasionally in Europe and the U.S.

The Devil and Daniel Johnston doesn’t really make a case for the worth of Johnston’s work in either medium—his genius is presented as a given. But his resurrection isn’t offered as much of a triumph, for the present-day scenes of him performing are more sad than inspiring. We know what he means when he refers to himself as a ghost of his former self. “It was my fate to become famous,” he says, “and also to be damned.” In a bleaker way than befalls anyone in American Dreamz, Daniel Johnston has been eaten alive by his own myth.