Today on Alex Bennett's radio show, a standup comic was on saying that
when comics heard that Robin Williams was performing at a club the same
night as them, they'd refuse to go on. He said that when he was first
starting out, he told Robin Williams his idea for immitating
celebrities immitating other celebrities and that he was planning on
doing Lawrence Welk (sp.?). If my memory serves, he immitated Lawrence
Welk cursing to immitated some other celebrity.
He said that Robin Williams act was prepared and that he didn't do as
much ad libing as people think and that he had writers.