I grew up watching Underdog. Although the series ended in 1973, it continued in reruns for many years after (at least through 1979-1980, when I remember watching it.)

Underdog always spoke in rhymes. Normally, he spent his time as "Shoe Shine Boy", and was just that. But when he took one of his super power pills, he transformed into Underdog and saved his love interest, news reporter Sweet Polly Purebred. His nemesis was usually Simon Bar Sinister (voiced by Allen Swift, who is a true living legend of animation voiceovers).

The storylines were always pretty much the same, but there was usually a lesson to be learned at some point in the show.

It didn't end there, however.

After Underdog had beat up Simon Bar Sinister for the 300th time, the show often segued into "Tennessee Tuxedo", a silly cartoon (also involving lessons learned) starring a penguin as the title character (voiced by Don Adams of "Get Smart" fame), his dimwitted walrus pal Chumley, and Mr. Whoopee, who would give them science lessons with his magic expanding chalkboard.

There were a number of other cartoons that ran along with Underdog, including one about 2 American soldiers in the old west tangling with two Native Americans (who would probably be seen as racially offensive today). I can't recall the others.

It was a great, fun kids show back in its day.