From some of these comments, I am guessing that some of you have never suffered from great depression.
It is a terrible illness. Many brave, intelligent people have had their lives destroyed by it.
Either he was not on meds, did not take his meds, or they could not find a pharmaceutical cocktail that worked for him. I guess that he suffered from depression his entire life. Can you imagine the roller coaster ride of Robin Williams? Lots of suffering took place during his life ... highs and lows.