The documentary delves into the mysterious life and musical legacy of Harry Nilsson, seeking to answer the question, “Who is Harry Nilsson?” It features both new and archival audio and video materials, including interviews with notable figures such as Robin Williams, Yoko Ono, Van Dyke Parks, Randy Newman, Ray Cooper, the Smothers Brothers, and Micky Dolenz. The film incorporates promotional clips, music videos, and home movies, as well as segments from an unreleased documentary filmed during the making of “Son of Schmilsson” (titled “Did Somebody Drop His Mouse?”). Additionally, it includes rare footage from Nilsson’s television appearances on his BBC specials, “The Smothers Brothers Comedy Hour,” “Playboy After Dark,” and an episode of “The Ghost and Mrs. Muir.”