In 1966, Jim Henson created this commercial for General Foods' Wheels, Crowns, and Flutes snacks. It never aired but is still notable as it featured the first appearances of several Muppets including the Wheel Stealer who would eventually become our beloved Cookie Monster. Later, he appeared in an IBM training film, seen below. From Wikipedia:
The "Crown-Grabber" was used in a sketch on The Ed Sullivan Show, in which he ruins a girl's beautiful day. Known from then on as the Beautiful Day Monster, he made a number of appearances on Sesame Street and The Muppet Show. The "Flute-Snatcher" turned into Snake Frackle, a background monster from The Great Santa Claus Switch and The Muppet Show.
In 1967, Henson used the "Wheel-Stealer" puppet for an IBM training film called Coffee Break Machine. In the sketch, called "The Computer Dinner", the monster (with frightening eyes and fangs) devours a complex coffee making machine as it describes its different parts. When he is finished, the machine announces the monster has activated the machine's anti-vandalism system, which contains the most powerful explosives known to man. The monster promptly explodes. This sketch was also performed in October 1967 on The Ed Sullivan Show. It was also later performed on the George Burns episode of The Muppet Show' using the Luncheon Counter Monster.
Two years later, Henson used a similarly-designed and equally ravenous monster for three commercials selling Munchos, a Frito-Lay potato chip. This time, the puppet was called Arnold, the Munching Monster. After the three ads were produced, Henson had the opportunity to renew the contract. He chose not to, because at that point he was working on Sesame Street — and that monster puppet was moving on to the next stage in his career. According to Frank Oz, in a later routine the then unnamed monster won a quiz show and for winning was "given the choice of $10,000 cash, a new car, a trip to Hawaii, or a cookie." He took the cookie and from then on he was Cookie Monster.