I remember when it first aired, I was in 4th grade (Kennedy was assassinated when I was in 3rd). Bob Denver was previously a star in "Dobie Gillis" as Maynard G Krebs, and quite popular, while Backus was of course the voice of the popular Mr. Magoo. The big mystery to me (even as a kid) was how there was never any sexual chemistry between the Professor and Mary Ann.