Sometimes the mysterious life of an artist can make us enjoy his work even more. That's definitely true of late Chicago artist Henry Darger. But what draws us to Darger, in addition to the quality of his output, is the sheer quantity of it. Oh yes, and the fact that nobody had any idea that Darger was actually doing anything productive in his one-room Lincoln Park apartment.

Filmmaker Jessica Wu digs into the life of Darger in her documentary, "In the Realms of the Unreal," narrated by Dakota Fanning ("I Am Sam") and with the voice of Larry Pine ("The Royal Tenenbaums," "The Ice Storm").

Born in Chicago in 1892, Henry Darger had a rough early life. His mother died when he was still young and his father entered a poor house not long after, which led to Darger's being sent to an orphanage, from which he ran away at age 17.

At the same time he began writing his novel, "Realms of the Unreal," which ballooned to a whopping 15,000 pages by the time he died in 1973. For years, the reclusive Darger worked as a janitor by day and wrote his novel and created expansive and detailed paintings on butcher paper. He had but one friend in his lifetime and he lived an extremely solitary life, having only some glancing contact with his neighbors. Those neighbors assumed Darger was little more than a lonely old man who talked to himself and kept to himself.

Luckily, Darger's landlord was artist Nathan Lerner. When Darger went into a home shortly before his death, Lerner entered the apartment and discovered a body of work that most authors and artists can only dream of.

Wu takes us behind the always-closed door of Darger's apartment to explore his life and his mind. But, best of all, she does a brilliant job of connecting the dots between Darger's own troubled and solitary life with the brilliant output of his vivid imagination and artistic sense.

Interviews with Darger's neighbors and footage from his apartment mingle with the only three surviving photos of the artist himself, photos of the various places he lived and worked and with period films about Chicago itself.

But, wisely, Wu gives pride of place to Darger's accomplished, if often-childlike art, often cobbled together from images he clipped, traced or copied from comics, newspapers and magazines.

"In the Realms of the Unreal" is a loving snapshot of a brilliant mind undetected by a world that is quick to assess people and assign judgments. Everyone that knew or met Darger deemed him a troubled, lonely old man. Little did they know he was an imaginative, talented, driven artist.

"In the Realms of the Unreal" opens Friday, April 1 at Landmark's Oriental Theatre.