The documentary explores the enigmatic life and music of Harry Nilsson in an attempt to answer the question, "Who is Harry Nilsson?" The film includes new and archive audio and film including interviews with Robin Williams, Yoko Ono, Van Dyke Parks, Randy Newman, Ray Cooper, the Smothers Brothers, and Micky Dolenz. "Who is Harry Nilsson?" uses promotional films, music videos, and home movies; segments from the unreleased documentary made during the recording of Son of Schmilsson (Did Somebody Drop His Mouse?); and excerpts from Nilsson's rare TV appearances in his BBC specials, the "Smothers Brothers Comedy Hour", "Playboy After Dark", and in an episode of "The Ghost and Mrs. Muir". Written by Roger Smith