Once upon a time, Marvel Comics got the comic book rights to, of all things, 2001: A Space Odyssey. Anyone who’s seen that movie knows it’s, well, an odd choice for any sort of adaptation for younger readers, but it still happened. It was also an ongoing series. Where do you take a story like that once you’ve recounted the story from the movie? This wasn’t Star Wars with the promise of ongoing adventures for the characters. Part of the answer for writer/artist Jack Kirby was to create a new character that would cross over to the main Marvel Universe, namely Machine Man.
That was not the only time a licensed character got into the main universe. That also happened with Bug.