User blog comment:Gcheung28/Fannotate the Latest Avengers: Age of Ultron Trailer/@comment-24895270-20141025200742/@comment-4651179-20141025202558

Kingping first appeared in Amazing Spider-Man but as is a bigger enemy of Daredevil, he's with Marvel Studios. Sabretooth first appeared in Iron Fist, but is Wolverine's nemesis, he's with FOX.

It's not about where did a certain element of the Marvel Universe appear first, but how is it tied to a certain franchise. In the case of Adamantium, Wolverine is the character it has stronger ties to, so it's with FOX.

There are actually no references to the X-Men in Avengers: Age of Ultron. They can't mention Magneto, or the word "mutant."