When I heard the news about Robin Williams, my first inclination was, "Yeah, that makes sense"
Comedians like actors, authors, and musicians..all creative types, are very often very depressed people. Greg Giraldo was funny as he'll, but a pretty depressed guy. Artie Lang, he's a guy who has fought depression his whole life. I think for a certain type of comedian, a lot of what they do comes from a place of immense personal pain. Jim Carey, Darrell Hammond, Marc Maron, Richard Lewis, a lot of these guys have had issues with depression, a lot of them came to comedy amidst a mist of childhood trauma and unresolved issues. And comedy by nature runs hand in hand with tragedy.
Obviously not a default setting or a broad brush you can paint all creative types with, but tortured genius isn't a stereotype because it is a rare thing. Robin Williams..it sucks. I hope he found peace in the end.