Letterman first met Williams—who would end up appearing on Letterman's show about 50 times—at the Comedy Store in Hollywood in the 1970s when both comedians were trying to break into the scene.
"In those days we were working for free drinks," Letterman said. "What you would do is you would go onstage and do your little skits and then you would come offstage and if there was a new guy coming on, you'd want to stick around and make fun of the new guy."
But when Williams—who told everyone he was Scottish—came on, everything changed.
"It's like nothing we had ever seen before, nothing we had ever imagined before," Letterman said. "We're like morning dew, and he comes in like a hurricane."
It wasn't until Letterman got his own show, however, that they became friends.
"He was always so gracious, and we would talk about the old times and never did he act like, 'Oh I knew you guys were scared because I was so good,' and it was just a pleasure to know the guy, and he was a gentleman and delightful, and even in the old days, he was kind enough to ask me to appear on his Mork and Mindy show," Letterman said.
Now this was a double-edged sword, because he did it only because he was trying to help other fledgling, starting out comics. The other side of the sword is I had no business being on that show—I have no business being on this show. But he was nice, he gave me a job. And in those days, jobs were hard to come by. And there I was, and I was on "Mork and Mindy" and I can remember between the dress rehearsal and the actual taping of the show, the director of the program, Howard Storm, comes up to me and he says, "Well, you've been trying all week. This is your last chance.'"
So even to the detriment of the show, Robin was kind enough to invite me to come on because he thought, "Why can't I spread this around and have some of my friends share in my success," which is exactly what he did.
"Beyond being a very talented man and a good friend and a gentleman, I'm sorry, like everyone else, that I had no idea that the man was in pain, that the man was suffering," Letterman said. "But what a guy, Robin Williams."