The AV Club interviews director Terry Zwigoff about his movie Crumb (and some other stuff). From the interview–
The idea was to do a documentary on the three Crumb brothers. It was never a documentary about Robert Crumb in my head. I had met Charles and Max and liked them both, and I collected artwork from all three brothers. I even spent a night at their parents’ house, and met his father when he was still alive. So it started taking shape in my mind, and it seemed to me like a good idea for a film if Robert would do it. Not so much because I had access to Robert and he was willing to cooperate, but because I felt comfortable knowing that as his friend, I’d been exposed to facts that other people wouldn’t have known. And there were some things Robert never even thought to tell me about, not because he was trying to withhold information from me, but because he couldn’t tell what would be interesting and what wouldn’t. He couldn’t be objective about it.
Here’s a clip from the movie–