There's a Kickstarter-funded documentary coming out called Stripped about comic strips, which has an audio interview with him. I'm amazed and cannot fathom how they got that, as he's notoriously reclusive, supposedly even more so after he stopped writing Calvin and Hobbes.
There is a second Kickstarter to help cover the cost of purchasing the rights to additional footage ("Charles Schulz' TV specials, interview clips from Carson, 1930's newsreels and more"). It sounds like it's going to be very professionally done. Estimated delivery date is Dec 2013: http://www.kickstarter.com/projects/sequential/stripped-the-...
