That was Fett's first appearance in anything SW related and his figure launch as a mail in special was because of his introduction in the Holiday Special. However, I wouldn't say that they "created" him. Lucas probably told them to include this guy that his staff conceived complete with tech specs. Much like how GL told Tartakofsky (sp?) that they needed to include his character Asajj Ventress in the animated Clone Wars series. The CL creators did not create Asajj, they just introduced her.