My Grandfather met Robin Williams-it was about six months before Mork and Mindy, and he, along with 21 other people from his college class, had to do an interview with Williams, who would play out a different character for each of them. He had to do the class in order to get a job with a radio station (he later became the DJ at KZAP). It was amazing-he went seamlessly from character to character, voice to voice, and nailed all of them. My grandfather got "dejected", so Williams would look at his feet and mumble for every question, while my grandfather would try to get a straight answer from him.
Other than that, though, this man made me laugh nearly every time I saw him on a screen. His improvisational skills were the stuff of legend. Hollywood lost one of it's all-time greats today.