Jared Leto in ‘Chapter 27’

Although he began his career as “My So-Called Life’s” adolescent object of desire, Jared Leto’s work since has been marked by a kind of reverse vanity. The uglier the role, the better.

It began with “Fight Club,” where Leto’s angelic visage was reduced to a mass of scar tissue. In “Requiem for a Dream,” his arm turned black and purulent, and in “Lonely Hearts” his snappy fedora masked a wicked receding hairline.

To be sure, not all of Leto’s characters are hard on the eyes. There’s “Alexander’s” dreamy Hephaistion, for one, whose thighs brought down an empire. But there’s no question that he favors obsessives, driven by needs they can never fill, whether they’re damaged from without or only within.

So, does Leto, perchance, relate to the monomaniacs he’s so fond of playing? No such luck. “The parallel is that they’re incredibly challenging, and present a really unique opportunity to push myself and see how far I can go in one direction or another,” he says.

Oh. Still, the lengths to which Leto went for his latest role might seem just a tad extreme. To play John Lennon’s assassin, Mark David Chapman, in J.P. Schaefer’s new indie film, “Chapter 27,” opening in limited release Friday, Leto packed 67 pounds onto his lanky frame to better approximate the killer’s doughy physique. By the end of filming, the extra weight had taken such a toll that he could no longer walk to the set.

It’s easily his most dramatic transformation to date.

“I’m not sure it was the wisest choice,” he admits. “A friend of mine was recently going to gain weight for a film, and I did my best to talk him out of it. Just because you can lose the weight doesn’t mean the impact it had on you isn’t there anymore.”

The abruptness of Leto’s weight gain gave him gout and a doctor’s recommendation to take Lipitor. But Leto says slipping into Chapman’s skin was the best way to understand him. “The script didn’t say, ‘Page 1: You gain 67 pounds, and you’re miserable for two months.’ But as I started to research, I realized that the physical representation of this guy had so much to do with who he was.”

Leto, who these days spends more time touring with his band, 30 Seconds to Mars, than he does on film sets, laces his answers with spontaneous condemnations of Chapman’s homicidal fandom. But as an actor, he put such judgments aside. “As unfortunate as it can be to hear this, he was a human being,” Leto says. “A failure of a human being. A very sick and disturbed individual. But when you’re an actor playing a part, you don’t play a monster. Or at least I don’t know how to do that. You have to try to understand the human being there.”

In addition to changing his body, Leto altered his voice to echo Chapman’s eerily courtly Southern drawl. “He was very bottled up and you could hear it in his voice,” Leto says. “Everything was closed off. He barely ever speaks above a whisper and everything is kind of choked off in the throat. He was, in the strangest way, a very polite, genteel kind of person, and he certainly thought of himself as a gentleman, which is so strange for someone committing such a horrifying and despicable act.”

Leto relied on interviews with Chapman, who is serving a sentence of 20 years to life at Attica prison near Buffalo, N.Y., for reference, and on audiotapes recorded by an elderly librarian the actor met during a visit to Chapman’s hometown of Decatur, Ga. “I pored over that for hours and hours,” Leto says. “You can’t find someone in this day and age who talks like this. It’s kind of from another time.”

Chapman had many obsessions, not just Lennon and the Beatles, but “The Catcher in the Rye” and “The Wizard of Oz,” both stories of young people adrift in worlds they cannot comprehend. As Leto plays Chapman, he seems like a child not just in his timidity but in his explosive rages, to say nothing of his unhealthy attachment to a pop star. (The movie’s title refers to Chapman’s belief that he was carrying on the ideas laid down in J.D. Salinger’s “Catcher.” The book has 26 chapters.)

Next for Leto is Jaco van Dormael’s “Mr. Nobody,” a surrealistic time-travel odyssey in which Leto plays 12 versions of the same character, “including a 120-year-old man and a Neanderthal.” Among those personae is a role that even Leto finds intimidating: a normal guy.

“I wasn’t playing a drug addict or a psychopath, but one of the characters is married with kids,” he says. “Playing a father was one of the more terrifying things that I’ve had to do on film.”