The term “outside artist” has never been so apropos, or so wistfully sad, as it is in the case of Henry Darger, who spent his childhood in a home for “feeble-minded children” and his adulthood in near seclusion, working as a janitor and, in secret, on a 15,000-page novel with accompanying — and epic — illustrations. Even those closest to him, relatively speaking — his landlady and a neighbor, who cannot even agree here on the pronunciation of his surname — did not know about his work until after he died at age 81, when the fantasy world he lived in came to light. Now documentarian Jessica Yu gives us an extraordinarily respectful portrait of this strange, childlike man, as insightful as it can be about a loner who “only had conversations with himself” and revealed his innermost yearnings only through his work. His static illustrations, naive, comic-book-y collages executed in vivid color on 10-foot-long strips of butcher paper, come to hypnotic life, animated like something Terry Gilliam would have done in his Monty Python days, whimsically odd images of naked children with wings and little girls with penises that could feel pedophilic but never do, perhaps because, matched with excerpts from his novel, The Realms of the Unreal, read by actor Larry Pine, they reveal only innocent yearnings to both protect children and reject the adult world that has rejected him. This is an enthralling film, one that revels in its curious quest to understand a mind unlike anything most of us will ever encounter, and one that remains undeterred by the lack of answers to be found.