Watterson didn't want to turn down his first possible syndication deal, but he also didn't want to give up control over his own characters. So he rejected the offer. Eventually, United Features Syndicate bought the strip anyway. As the strip grew in popularity, Watterson began to get offers to license the characters for toys, T-shirts, greeting cards, and movies. He could have made millions from all the merchandising opportunities, but he refused all offers. He said, "My strip is about private realities, the magic of imagination, and the specialness of certain friendships. [No one] would believe in the innocence of a little kid and his tiger if they cashed in on their popularity to sell overpriced knickknacks that nobody needs."
This is why I always grit my teeth when I see a sticker on the back of a car window showing a little Calvin rip-off kneeling at the foot of a cross, or peeing on a Honda (when the car's owner drives a Toyota). Not only are they stealing Watterson's idea, but they are violating his deeply held principals.
Stepping off my soapbox now!