Budd Friedman is a fairly famous name in New York City, having opened the famed Improvisation Comedy Club, where he MC'd for many years as up-and-coming comedians like Jimmy Fallon and even Robin Williams tried to make a name for themselves. He recently wrote a tell-all novel full of antics, including the time Johnny Carson got drunk at a show. A story in the book, The Improv: An Oral History of the Comedy Club that Revolutionized Stand-Up, also claims that Robin Williams often stole jokes while he was still doing a lot of stand-up.
It's not Friedman himself who is making the charges, but fellow comedians Richard Lewis and Robert Wuhl, who mentioned in the book that anything funny Robin Williams heard stuck in his brain like glue, only to be regurgitated later. According to The Improv (via THR), some people actively disliked Robin Williams because of this trait, but Richard Lewis also seems to be somewhat defensive of the actor and comedian, noting,
Some comics hated him for it. But I wasn't one of them.
This isn't the first time that Robin Williams potentially using other comics' material has come up. In the book Comedy at the Edge, there's a story about David Brenner getting mad at Robin Williams for using some of his material and about Bob Shaw also confronting the comedian for using his material. Back in 2010, on Marc Maron's WTF Podcast, Robin Williams talked about loving to just get up and do improv on the stage, also noting that sometimes he would inadvertently pull information from other comedians when hanging out in the clubs. But he learned his lesson... and paid for it. Per what Williams said,
I think in the old days, if you hang out in comedy clubs, when I was doing it almost 24/7, you hear things and then if you're improvising you almost all the sudden you repeat it, going, 'Oh shit.' My brain was working that way. And then I went through a period where I had to go, 'I'm not going to hang out [in comedy clubs] anymore. I can't, because I don't want to be getting into that thing.' I was also like the bank of comedy where I was like, 'Shit, here you go.' I paid shitloads of cash and was like, 'I'm sorry.' There's some stuff that's common material, and there's other stuff you go, 'fuck, I'm sorry.'
Comedians get accused of stealing jokes more often than you might guess. This has even happened recently when popular female comedian Amy Schumer dealt with accusations, but she's certainly not the first or last comedian to ever court controversy as a celebrity. Sometimes people really do blatantly steal jokes, and sometimes people have jokes that are simply similarly formatted or inadvertently lifted from something the comedian heard in the past. There's a lot of grey area when it comes to putting together a set--especially when it's improv-heavy--and the fact of the matter is that Robin Williams is no longer with us to tell his side of the story in regards to what happened with the likes of Richard Lewis and Robert Wuhl.