Those who recall Jake Gyllenhaal’s breakthrough performance as “Donnie Darko” in 2001 might have a tough time reconciling that little-boy-lost character with his pumped-up prizefighter in this year’s “Southpaw.” The latter work conjured the kind of body-and-soul transformations associated with Robert De Niro in his prime, or another child actor-turned-leading man, Christian Bale.

In his review for Variety, Justin Chang wrote: “You can practically smell the blood, the sweat and the fierce actorly commitment rising from Jake Gyllenhaal’s bruised and tattooed body.”

Gyllenhaal’s role in “Nightcrawler,” barely a year prior, went in the opposite direction physically, with his nocturnal prowling cameraman with a nose for carnage looking gaunt to the point of sickly.

The 35-year-old actor, Variety’s Intl. Star of the Year, offers that it’s “important to have an audience enter a movie being excited about what the actor has done to prepare for a role.” But it goes deeper than adding or dropping bulk. The external bleeds into the internal.

“You start seeing the world in a different way and pick up clues for the character,” he says, “and that all goes into the final result. I’ve just discovered over the past three years that a lot of that can also be physical, but it doesn’t just work in a physical way. I can’t just go and learn how to box and then that’s my character.”

A conversation with Gyllenhaal suggests he’s a human sponge, absorbing information wherever he can find it. For “Southpaw” he drew inspiration from the Puerto Rican welterweight Miguel Cotto (“he’s been through a lot in his career and his style is particularly intoxicating”); and for the predatory Louis Bloom in “Nightcrawler,” he happened upon the idea of a coyote. “I just couldn’t get it out of my mind,” he says. “And I thought: ‘Well, what do they look like? How do they move? How do they act?’ They’re ruthless. And that was Louis Bloom at the time, and it felt right to me.”

But Gyllenhaal can go minimal without losing his trademark intensity. In the upcoming “Demolition,” from French-Canadian director Jean-Marc Vallee (“Dallas Buyers Club,” “Wild”), he plays an investment banker who struggles with the loss of his wife from a car accident, throwing him into an existential spiral. It’s a story about dealing with grief and the void that can exist at the center of one’s soul when feelings are difficult, if not seemingly impossible, to grasp.

“I recognized that a performance can be very quiet and maybe can just have a rumble underneath but be equally expressive,” he says. “We were moving toward the opposite of instincts and what convention would tell you, which is what the movie is about — that any form of loss is relative. And your expression of whatever that is is defined by the individual.”

In a way, Gyllenhaal’s volatile loner who is haunted by visions of the apocalypse in “Donnie Darko” established a kind of template for the sad-eyed actor who seems to gravitate toward characters who are damaged, unstable or seemingly inaccessible. It’s not exactly the kind of type-casting that keeps Gyllenhaal up at night, just as he’s likely not bothered by his image as a sensitive dreamboat. The actor has played his share of troubled boy toys who experience reckless affairs with older women in “The Good Girl,” “Lovely and Amazing” and even to an extent in “Nightcrawler.”

“It’s about what we consider to be damaged,” he says about his off-kilter array of characters. “Often I find people who are honest in their expressions healthier than people who are trying to hide it. So I’m drawn to those characters who are expressing those feelings. The reason why ‘Donnie Darko’ was interesting to me was because there was a slew of movies at the time when it was all about whether you were a nerd or a jock, and who’s going to kiss the girl.

“So the ‘Donnie Darko’ character to me felt like a very honest expression of what adolescence really feels like.”

If Gyllenhaal’s Louis Bloom in “Nightcrawler” is all obsessive neurosis and self improvement-spewing dogma, his role as the doomed mountain climber Scott Fischer in “Everest,” released in September, is characterized by utter repose and even a sense of grace when faced with his own mortality.

“It didn’t really all coagulate until I met his children,” explains Gyllenhaal about his research for the real-life adventurist/guide. “Ultimately their dad was a guy who didn’t really hold people’s hands. That universe was going to deliver what it was going to deliver and there was no other experience like climbing that mountain. You could have a clear day and then within moments, not. And wherever you were, that was your gamble.

“I was also reading ‘Man’s Search for Meaning’ at the time (in which) Viktor Frankl writes about how you don’t get to choose when you die. And that’s what Scott believed. Because of that he decided to live in the present in a way that was really inspiring to me. He wasn’t burdened by the fear of dying.”

Over the course of his roughly 25-year career, Gyllenhaal has worked with some of the most accomplished directors in the business. In addition “Everest’s” Baltasar Kormakur and “Demolition’s” Vallee, he has experienced fruitful collaborations with another French Canadian, Denis Villeneuve, on “Prisoners” and “Enemy”; seized the lead in David Fincher’s “Zodiac” as a newspaper cartoonist-turned-amateur sleuth with a cast that included Robert Downey Jr. and Mark Ruffalo, no less; inhabited the role of a grunt in “Jarhead,” Sam Mendes’ attempt to do for Desert Storm what Stanley Kubrick did for the Tet Offensive in “Full Metal Jacket”; and played opposite Heath Ledger in Ang Lee’s celebrated cowboy romance, “Brokeback Mountain,” considered a breakthrough treatment of gay themes even by boutique-distributor standards, earning Gyllenhaal an Oscar nomination in the process.

Unlike a lot of actors who take a stab at stage work to check off their bucket list, Gyllenhaal — who has called New York his home for the past five years — appears fully committed, having made his Broadway debut early this year in Nick Payne’s “Constellations” (the New York Times’ Ben Brantley called Gyllenhaal’s performance “a magnificent work of understatement”) and taking a stab at musical theater in the Encores! production of “Little Shop of Horrors.” (He made his theatrical debut in London’s West End in Kenneth Lonergan’s revival of “This Is Our Youth” in 2002.)

When asked if he would like to direct, Gyllenhaal responds in the affirmative without missing a beat. But for now he’s happy seizing the reins as a producer (a role he played on “Nightcrawler”), having just launched his own production company and signing a first-look deal with Bold Films, the shingle that co-financed and produced “Nightcrawler,” and the outfit behind last year’s “Whiplash” and Ryan Gosling’s debut as a writer-director, “Lost River.”

“We’re up and running,” says Gyllenhaal. “Producing is the next step for me but hopefully, eventually directing.”