At four, Robert Crumb would hump his mother's cowboy boots while singing 'Jesus Loves Me'. At six, he developed a sexual attraction to Bugs Bunny. At 17, he became driven by an obsession: to take his revenge on the alpha-males of his school by going down in history as a great artist. Crumb was an unlikely hero of the '60s counter-culture, but strips like Fritz the Cat, Mr Natural and Keep on Truckin' made him the toast of Haight-Ashbury. More interesting still is his later, confessional work, analysed and berated in the film by a series of female comic pundits and ex-girlfriends. So far, so good, but when focusing on Crumb's relationship with his two brothers the documentary occasionally goes off the rails to become a prurient, though undeniably fascinating, freakshow. Still, it remains an outstandingly interesting portrait of obsession and genius.