In 1959, the Kellogg's people decided to bring out their version of Cheerios, which was the most popular cereal from their competitor, General Mills. They added a "K" to what was basically the same thing and called it Kellogg's OK's.
Originally, the product's mascot was a burly Scotsman named Big Otis. I have no idea why they thought kids would spark to the character and I'm guessing that someone at Kellogg's was afraid they'd made a bad call on that one. Almost immediately, Yogi Bear became co-spokesperson for OK's and before long, Otis was off the box and the bear was in his place. I'm also guessing that Kellogg's had their highest hopes for this cereal and that as they assigned other Hanna-Barbera characters to appear on cereal boxes and in commercial, they saved H-B's most popular star, Yogi, for the most important assignment.
Yogi may have been smarter than the average bear but he wasn't much good at selling cereal. In the early sixties, Kellogg's decided to give up and discontinue OK's. Their product development team was asked to come up with a new product that could use the same manufacturing equipment…and that's how Froot Loops were born.
This is a commercial that I recall as the one that introduced OK's, at least in the Los Angeles area. Since Yogi liked it, I immediately asked my parents to get a box, which they did. I liked it but I liked Cheerios more. Apparently, I wasn't the only kid who made this decision.