You might not recognize him right away, since he doesn't have the glasses he'd begin sporting a few years later, but "Mr. Marvel" himself, Stan Lee, made the first of two appearances on To Tell The Truth in this syndicated episode from 1971. Stan appears in game 2, so we'll just have to navigate through the 1st game before we get to him.
Funny thing. Dick DeBartolo, a long time writer for Mad Magazine, was a writer for Truth during this period. Ya wonder if maybe Stan was trying to lure him to Marvel?