Underdog Cheerios Commercial
A 1965 cereal commercial for Cheerios featuring Underdog, actually serving the purpose for which was originally intended for-- Underdog (along with a stable of other cartoon characters) was designed by the Dancer Fitzgerald Sample advertising agency in 1960 for cereal producers General Mills to sell cereal, it was only after he became the break out star did his adventures branch out a bit.
Via Cartoon Brew