You probably don’t know the name Emile Hirsch. Not yet at least.

He’s a young, good-looking, up-and-coming actor who’s been working steadily for the past few years now – he was the guy who lusted after Elisha Cuthbert in “The Girl Next Door”; maybe that’ll ring a bell.

All that should change, however, with “Into the Wild,” and deservedly so.

Hirsch offers a tour de force as the doomed Christopher McCandless, whose restless wanderings in search of nature, beauty and truth left him dead in Alaska, starved and alone, at 24.

In adapting Jon Krakauer’s 1998 best-seller of the same name, writer-director Sean Penn gives him a wealth of material to work with. Hirsch gets to be charming, passionate and idealistic but also impetuous, stubborn and self-righteous. Penn depicts this flawed figure with all the richness and complexity you’d find in the unforgiving Alaskan terrain, presenting McCandless in both his selflessness and selfishness without once judging him or turning him into a martyr.

At the same time, there’s an innocence to “Into the Wild,” with its notions about the purity of freedom, that harkens to films of the late 1960s like “Easy Rider.” And Penn, working with cinematographer Eric Gautier (“The Motorcycle Diaries”) and sometimes shooting his own footage, captures the grit and grandeur of this nation so vividly, he almost makes you want to chuck it all, too, and head for the open road.

That’s Chris’ plan in 1990 after graduating from Emory University. He suggests to his status-conscious mom and dad (Marcia Gay Harden and William Hurt, both strong in just a few flashback glimpses) that he’s interested in Harvard Law School, and already has saved $24,000 toward tuition.

Then he ends up giving the bulk of his money to charity and burning the rest of his cash, literally, before hopping into his beat-up car for points unknown. He aspires to be a modern-day Thoreau or Jack London, communing with the wilderness and coming out enlightened for the experience, and even adopts the name “Alexander Supertramp” to signal his bold, new persona.

But he’s clearly still mired in adolescence in many ways; his journal entries – rambling, self-important – include oversized exclamation points dotted with little circles at the bottom. That boyish enthusiasm often works to his advantage, though, especially as he enjoys the kindness of strangers during his travels.

There’s the hippie couple (Catherine Keener and Brian Dierker) who take him under their wing and treat him like a son; a South Dakota farmer (Vince Vaughn, comparatively subdued) who gives Chris a job and provides him with a de facto home base; a teen folk singer (Kristen Stewart) who takes a liking to him at the Southern California vagabond mecca of Slab City; and, most significantly, a lonely retiree (Hal Holbrook) who tearfully, touchingly becomes his one true friend. (Not everyone is so generous; his trip to Los Angeles turns into a night in hell.)

As he nurtures his own spirit, though, he doesn’t seem to care that his mysterious, two-year absence has destroyed those of his parents, whom he describes as liars and hypocrites. He’s also failed to keep in touch with his younger sister, Carine (Jena Malone), who was his steadfast ally and whose wistful, worried monologue serves as the film’s narration. (Penn relies a bit too much on this device, as well as printing Chris’ words in capital letters on the screen; on the flip side, original music from Eddie Vedder complements the action beautifully.)

Penn never shies away from the bleaker aspects of the story – not just in the external surroundings but within the character’s soul. Hirsch lost 41 pounds from his already lean frame to play the man at his most mortally emaciated, but in Penn’s assured hands, the actor’s transformation from the inside is just as startling to behold.