Jake Gyllenhaal for Details Magazine

Actor Jake Gyllenhaal dons a full beard as he appears on the September issue cover of Details Magazine. He is photographed by Mark Seliger. 

From Details.
A dozen Jake Gyllenhaals pass by me outside En, the mobbed Japanese bistro where the actor has booked us a table. Some of these doubles are brainy types, a Gyllenhaal staple since Donnie Darko launched him to indie stardom at 20 and most recently seen in the existential sci-fi thriller Source Code. Others mimic the hyper-fit versions of Body by Jake: the ripped Marine of Jarhead, the ex-con of Brothers, the pharma rep who showed so much ass in Love and Other Drugs. There's even a Prince of Persia Gyllenhaal, of the anime abs and shaggy hair. Granted, this is New York City's trendy lower West Village, where the good-looking go to dine on Friday nights. And part of Gyllenhaal's appeal has always been his Everyman-ness. Still, the sheer number of replicants is surprising. 
Or maybe it's just me. As Gyllenhaal's body of work grows, he only gets harder to peg. A-lister, art-house thespian, indie king—he's simultaneously all and none of the above, a distinction that's kept him just shy of Leo/Brad one-name status. That's likely to change after this month's End of Watch, in which Gyllenhaal gives a performance, as a South Central L.A. cop, unprecedented in its pure exposure of the man. I actually extend a hand to greet a passing six-footer with the exact buzz cut and MMA-esque physique Gyllenhaal has in the film, until the man's glare tells me this will not be our Brokeback Mountain moment. It's almost a letdown when the genuine Gyllenhaal hops out of a cab—scruffy-bearded, in a blue work shirt, off-brand sneakers, and drab tan chinos that nullify any shot at a memorable first impression.
I understand the beard is for the role—roles, actually—in the movie he's currently filming in Toronto, An Enemy, in which he plays a nerdy history professor obsessed with a vain actor who's his double. But as we order a degustation menu, I start by asking him where the muscle-bound cop of End of Watch has gone. Gyllenhaal has been spending more time in New York recently, and gossip columns had the lifelong fitness nut leading spinning classes at SoulCycle and riding his bike to and from meetings, but— 
"I haven't cycled in a long time," he preempts. "Ask me where I run." 
"Where do—" 
"I don't run anymore. Do I take care of my body and take conditioning seriously? Yes. But exercising regularly doesn't fit the energy of the character I'm playing now."
A beer arrives for him, half of it vanishing in the time it takes me to get the tape recorder going, and as the first three of our ten delicate courses slowly arrive, Gyllenhaal's plates empty fast. A suspiciously large number of beautiful waitresses deliver the respective courses, glancing sideways at him as they linger over descriptions of each dish and continually align fresh sets of chopsticks. That's the only clue I'm sitting with a celebrity. 
Gyllenhaal's essentially in character as we meet, though it will take me some time to understand that and what it means to him. Oblivious for now, I remind myself how long his day's been already: a full morning on-set in Toronto, then the flight back to New York, then a battery of meetings right up to our dinner. Tomorrow will be busier: auditioning aspirants for various parts in his American stage debut, If There Is I Haven't Found It Yet, which opens Off Broadway this month, then a late flight back to Toronto for a full Sunday of shooting An Enemy.
It's still not entirely clear to me if he's playing both main characters in the film: the professor and his doppelgänger, the actor. "No," he says, "it's a movie about me meeting myself, but another actor's playing me." He delivers the line with such sincerity, I miss the sarcasm for a second—long enough for the ice to break with Gyllenhaal. Sarcasm normally induces discomfort and introduces distance, especially between people newly met. With Gyllenhaal it somehow does the opposite—he brings you in on the joke, puts you at ease. Is it because he's really that genuine and positive? Whatever the quality is, it's of increasing value to him. 

"My whole life," he says, "I'd come to a scene and just ask for something real. I'd say, 'Please, just tell me what's going on. All the research, how your character picks up a fork, it'll all come when we know the truth.'" He's talking about a personal and professional evolution that accelerated during the months of his preproduction involvement in 2011's Source Code. The story—a soldier is enabled by technology to relive eight crucial minutes, over and over, until he gets it right and saves the world—resonated deeply with him. "Now the time's come to turn that on myself"—searching, over and over, for the truth—"and it's 'Game on.'"

There is more at Details.