As a cult filmmaker in the late ’70s and early ’80s, Howard Brookner was a rising Hollywood star. As a documentary director, he tackled subjects like the enigmatic William S. Burroughs, but Brookner’s career was cut tragically short in 1989, when he died of AIDS.

But 23 years after Brookner’s death, his nephew, Aaron Brookner, unearthed more than 300 cans of Howard’s film in Burroughs’ New York City bunker. Not only did this footage include outtakes from Howard’s 1983 doc Burroughs: The Movie, but they offered a glimpse at Howard’s life, from rehearsing with Madonna for his first Hollywood feature to his own personal struggles with his illness. Now, Aaron Brookner’s documentary unearths who his uncle was, both as a filmmaker and a human being.

Uncle Howard will premiere in competition at the Sundance Film Festival, which runs Jan. 21 through 31. Watch the exclusive trailer above.