He was a phenomenal comedian. I read several pieces about him that all sated in was a bit of PIA to work with. Not that he was mean or arrogant but because he could not stay on script to save his life. He would add lib all the time. I think I recall reading about "Aladdin" that the writers just gave up, let him loose and did the animation afterward to match his dialogue. Seemed to have worked out very well. Same for his stand up, I do not think he ever did the same routine more than once because he had no routine.
I remember laughing my but off watching Mork and Mindy.
I wish he could have found the help he needed.