Todd Phillips’ origin story of Batman’s most persistent nemesis is expertly crafted and features a stunning lead performance, but it’s also a morally problematic exercise in cinematic nihilism. You won’t be easily able to forget Joaquin Phoenix’s mesmerizing turn as “Joker,” every bit as impressive as Heath Ledger’s, which won that actor a posthumous Oscar—Phoenix could well be honored with a nomination, even if the award eludes him. However, you will likely find the film itself just as hard to forget, though you might want to despite its technical sophistication.

The narrative fashioned by Phillips and Scott Silver is actually quite simple. In a dystopian Gotham that looks alarmingly like early 1980s New York City beset by a damaged economy that resembles the U.S.A’s in 2008, Arthur Fleck (Phoenix) is a mentally challenged young man with a propensity to break out in uncontrollable fits of laughter; he works for a service that furnishes clowns for parties and other events. Otherwise he’s devoted to caring for his ill mother Penny (Frances Conroy), who once worked for the family of the city’s top citizen Thomas Wayne (Brett Cullen) and remains devoted to the man.

The activity on which mother and son most enjoy spending time together is watching a late-night talk show hosted by an iconic but nasty host named Murray Franklin (Robert De Niro). Arthur dreams of appearing on the show, being called from the audience down to the stage and praised by Franklin while the audience applauds; he also thinks about doing stand-up at a comedy club. Meanwhile, though, the city’s budget cutbacks end his sessions with a social worker (Sharon Washington) despite the dark thoughts she finds in his journal, and close off his supply of the medication he needs to stay in at least some degree of self-control.

But despite an apparent relationship he develops with an attractive single mom (Zazie Beetz) down the hall, Arthur’s problems only escalate as he runs into trouble at work. When a gang of young toughs harass him as, in his clown getup, he advertises a store’s going-out-of-business sale on the sidewalk, stealing his sign and beating him with it, he’s harangued by his boss, who threatens to take the cost of the sign out of his pay. Gruff co-worker Randall (Glenn Fleshler) gives him a gun so he can defend himself in the future. When he accidentally drops it on the floor during a performance at a children’s hospital ward, it gets him fired; but it also comes in handy when he’s accosted by three young Wall Street types on the otherwise deserted subway and he uses it to kill them all, “Death Wish” style. It’s his first turn to violence, but hardly the last.

From that point Arthur becomes increasingly unhinged—as does the society around him. Reports of the killer subway clown offing a trio of over-privileged moneymen spawn a movement against what would nowadays be called the one-percenters who take advantage of everyone else. Donning clown masks, protestors take to the streets, and violence follows in their wake. Wayne, who has decided to run for mayor of Gotham, speaks out against their movement, a symbol of the hated establishment.

Arthur, however, is moved by personal rather than political motives. While he will revel in the chaos and anarchy his act has unleashed—appreciatively watching as the protestors waylay the two cops (Bill Camp and Sean Whigham) who are trying to question him about the subway killings—he is more interested in dealing with those who have, in his view, wronged him. They include his own mother, whose treatment of him as a child he eventually uncovers, and some of his old co-workers. And he also has a matter to settle with Wayne, whose son Bruce (Dante Pereira-Olson) he briefly encounters, along with the boy’s protective butler (Douglas Hodge).

And then there is Franklin, who ridicules Arthur’s humiliating attempt at stand-up by showing clips from it on his program. Seeking to profit further from the guy’s misery, Franklin invites Arthur to appear on his show—which he does, in full Joker guise. It turns out to be the beginning of his storied career as a ringmaster of mayhem.

Phoenix is rarely off-screen for the entire running-time of “Joker,” looking emaciated and grotesque, and it’s hard to tear your eyes from him, even when the character is engaged in the most gruesome business. It’s a magnetic turn, even though you might wish the polarity were reversed—showy and insistent to be sure, but undeniably creepily effective. The unsettling thing is that it’s good enough to elicit more than a little sympathy for the character—who is, after all, bullied and brutalized into becoming the champion of chaos that the Joker ultimately is. Encouraging us to cheer him on is perilously close to approving of, if not advocating, what he does. It makes for a troubling sensation.

The other major players—Conroy and De Niro—provide able support, with the latter obviously relishing the chance to turn the tables on his role in “The King of Comedy,” a film which (along with “Taxi Driver”) Phillips is obviously paying homage to. Beetz is an attractive and likable presence as Arthur’s supposed romantic interest—while also capturing the character’s understandable fear when required, while among the other cast members, Leigh Gill will strike a chord with the audience as the office manager whose recoiling over one of Arthur’s most brutal acts perfectly mirrors our own reaction.

On the technical level, “Joker” is outstanding in every way. Using a blend of locations and sets, Mark Friedberg’s production design creates an extravagant atmosphere of urban life gone to seed and Lawrence Sher’s cinematography accentuates the effect, while Mark Bridges’ costume design—especially in Joker’s last-act outfit—and the work of the makeup artists are similarly superb. Jeff Groth’s editing gives Phoenix ample opportunity to make his mark in scenes, for instance, of ghoulishly sinewy dance while bringing in the film at a relatively trim two hours, and Hildur Gudnadóttir’s score avoids conventional bombast; the pop music intrusions are spot on, too.

But despite the extraordinary degree of skill on display throughout “Joker,” the movie is dismaying, not just for its explicit displays of carnage—parents, this is not a comic-book movie for kids!—but its detached attitude toward a misfit’s descent into madness and violence, a reality all too common in today’s society. One can admire its cinematic virtuosity while wondering whether, like “Natural Born Killers” and “V for Vendetta” before it, it’s not really an irresponsible piece of work on a broader level.