Rainer Werner Fassbinder would have been 70 this year, though it’s impossible to imagine the uncompromising German director, writer, and actor cloaked in a mantle of respectability. It was his destiny, and his determination, to push buttons and challenge taboos until his heart unexpectedly gave out in 1982. A charismatic character — openly gay in the movie business when that was still a radical act — who inspired and exploited the adoration of his collaborators and lovers, Fassbinder left a legacy of some 40 discomfiting features and two remarkable miniseries — as well as a lingering mystery about the source of his obsessiveness.

Danish filmmaker Christian Braad Thomsen, who befriended Fassbinder after the chilly reception to his feature debut, Love Is Colder Than Death, at the 1969 Berlin Film Festival, examines the complicated artist’s life and work from a psychological standpoint, empathetic but warts-and-all. Drawing on strikingly candid recent conversations with key intimates such as actress Irm Hermann and actor and assistant director Harry Baer, as well as rarely seen interviews he filmed with Fassbinder in the 1970s, Thomsen crafts a riveting portrait of a spoiled boy, raised by disparate family members, who, as an adult, sought to create an ad hoc family of his cast and crew. Stuffed with scenes from Fassbinder’s brilliant, brutal films (his last, most overtly gay film, Querelle, is also playing in Frameline39), this bracing documentary illuminates how the director’s personality informed his art and galvanized his actors.