He certainly had an imagination I could only wish to have. It was him and another guy that came up with the D&D concept though not just him alone.
I wonder how much of his condition was due to stress. He left TSR, which he co-founded, because he did not agree with the direction it was going. Knowing that the next time I think about buying TSR I will remember him. Seems like a genuine guy who had his hand in many different rpg areas.
He was an apparently pretty cool but strange dude. I remember the debacle going on with him and TSR, and him leaving and I think he did a few different ones, but I remember his Dangerous Journeys (Dangerous something anyway) game, which was... I thought D&D was bad at the time! But this thing had Upper Body Strength, Upper Body Neural Control, Mental Alacrity, Memory, and all kinds of figured characteristics formulas and division... It was a nightmare just to look at it, I couldn't believe it! I played in one session and the GM and all of us were like "Mmmmm... Nnneeeehhh really don't think so."
I e-mailed him ten years ago and he actually replied to my question about how to pronounce his name (and of course did the fanboy 'squee! Thanks for D&D!'), because we had always called him "Guy-Gacks" but I had read somewhere it wasn't pronounced like that, and he confirmed it saying it was pronounced "Gee-Ogh", so some sort of weird pseudo-French property. He made a little joke but I can't remember it exactly, something like "GeeOgh, like BuffaLo" or something - some sort of livestock, I remember that. That was the only time I was in contact with him and of course no longer have that e-mail address or anything, sadly, I would have liked to have kept that message.
I found it hilarious that one of the very last things I read about him was that he had developed a distaste for complicated game systems and was convinced that simple, fast, intuitive rules-lite systems were really what he thought was the better choice for RPGs - this from the guy with a thousand different books full of rules and new lists and classes and stats for everything from Allah to Zardoz, the guy who makes you check for traps every 10 feet and has different XP progression charts for each different class... I don't know, I just laughed out loud when I read that.