One of the earliest superstars of Saturday morning television was Don Herbert, aka Mr. Wizard. Herbert enjoyed a remarkable 14 year run with Watch Mr. Wizard, airing on NBC from 1951-65, teaching two generations of children about science, something that today would be frowned upon in an era where kids are more interested in video games in whatever forum is available, be it on computer or on their XBox or other game console.
Since the show was based in New York, the inestimable Don Pardo, still chugging along on Saturday Night Live, is the announcer, but isn't heard in this sample episode:
Herbert would return for one more season, again on NBC, in 1971, with a Canadian produced series, titled simply, Mr. Wizard. I think I might have seen at least one episode of that, since it was airing around lunch time. Finally, there was one more revival, with Nickelodeon's Mr. Wizard's World in the 80's. This version tended to air more on weekdays than on Saturdays, and as such, I did happen to catch a few bits here and there. I was but a toddler at the end of the original series' run, but my rating applies to it as well as its later incarnations.