I was fairly young in the 60s, but I do remember What’s My Line, and the tail end of This Is Your Life in reruns, and up until the mid 70s talk shows that were more or less Hollywood studios advertising opportunities like Merv Griffin and Mike Douglas.
I really liked them, even though they were more or less sanitized unlike Geraldo and Maury and the ilk that are more for sensationalism.
John Daly was a mystery guest on the last episode. He had some fame as a game show host and a newscaster, he made first radio report of attack on Pearl Harbor on 12/07/41
I’ve watched a good number of the YouTube clips at various times and just now tried to find one where the celebrity’s voice was so well known that he (maybe she) did a great job of disguising it. No luck.