My chum Earl Kress — and I know enough not to doubt him about this kind of thing — says both I and most reference books are wrong. Frank Milano, he says, was not the voice of Mr. Wizard the Lizard on the "Tooter Turtle" cartoons seen on the 1960 King Leonardo cartoon show. Earl is certain that voice was supplied by Sandy Becker, the famed New York kid show host. I think Allen Swift played Tooter, so I don't know what voice on that series might have been done by Mr. Milano, if he even did a regular character at all. But his name appeared in the credits.
Interesting Note: The company that produced King Leonardo and His Short Subjects, as the show was originally called, was Total Television. Total later produced a number of other shows including Tennessee Tuxedo and His Tales (1963), Underdog (1964), The Beagles (1966) and Go-Go Gophers (1968) that featured new cartoons wrapped around reruns from their previous shows. As a result, Frank Milano, who passed away in '62, was credited as a voice actor (and presumably paid decent residuals) on shows produced years after his death. Nice work if you can get it…