Born in France and raised in prewar England, a sexually curious boy named Peter de Rome found a way to marry his two great loves: cinema and men. He captured the sexual adventures of friends and strangers alike on his Super 8 camera (remarkable in an age before cell phones and webcams); he then started showing his offbeat, playful, sex-positive underground films at house parties and private screenings in the early 1960s. These films’ groundbreaking erotic images soon made him a significant figure in underground cinema and a pioneering voice in the emergence of gay porn.

Courtly and puckish at nearly 90 years old when the documentary catches up with him, de Rome shares decadent, funny tales about admirers such as David Hockney, William S. Burroughs, and Andy Warhol — and reveals how his feature-length adult film Adam & Yves managed to capture the final screen cameo of Greta Garbo. Grandfather of Gay Porn is chock-full of both softcore and explicit clips from his artful short films (which span three decades), many of which have recently been archived by the British Film Institute for preservation.

As a portrait of a queer cinema visionary, who died just last year, this entertaining documentary charts Peter de Rome’s life and career as they unfolded alongside some of the most significant events in 20th century gay history, from the Stonewall riots to the decriminalization of homosexuality.