David Letterman knew Robin Williams for 38 years, and remembers him as a "very talented man and a good friend and a gentlemen."
On Monday's Late Show, the host paid tribute to his fellow comedian by showing clips of him on the CBS program and a personal photo of himself posed with Williams, Richard Pryor and Comedy Store owner Mitzi Shore.
Letterman went on about the Oscar winner's immense talent, recalling seeing him perform stand-up back in the day. "All of a sudden he comes up on the stage and -- you know what it is -- it's like nothing we had ever seen before, nothing we had ever imagined before. And then he finishes and I thought, 'Oh that's it, they're gonna have to put an end to show business because what could happen after this?'" he said. "Honest to God you thought, 'Holy crap, there goes my chance in show business because of this guy.'"
Becoming a bit emotional, the 67-year-old host added, "What I will add here is beyond being a very talented man, and a good friend and a gentleman ...I'm sorry, like everybody else, I had no idea that the man was in pain, that the man was suffering, but what a guy."
Williams passed away on Monday, August 11, of an apparent suicide. He was 63. The actor/comedian was on the Late Show 50 times.
Williams' wife revealed later that week that her husband was suffering from Parkinson's Disease.
Watch the video to see ET's own vintage footage of Robin before one of his appearances on Late Show.