Opening the same year as Iron Man, 2008's The Incredible Hulk has mostly been ignored in the Marvel Cinematic Universe. The Hulk still appears a lot, of course, including in Thor: Ragnarok, but the role switched from Edward Norton to Mark Ruffalo. You haven't seen anything of Betsy Ross (Liv Tyler), and it took nearly a decade before Thunderbolt Ross (William Hurt) re-emerged after being part of the post-credits scene that helped tease The Avengers. The biggest absence has been of the Hulk's villains, the Abomination and the Leader, who haven't been seen since.
Speaking with Crave Online, Marvel's Kevin Feige gave an explanation for why we haven't seen the Hulk's enemies since they were defeated...
"It is an embarrassment of riches of places we could go or characters we could reprise or bring back now that we’re… I think Ragnarok is our seventeenth MCU film. And you would be surprised how many… it’s come up. It’s come up. Just finding the right place. And as I said, if you can’t do it right, don’t do it or do it later, and the notion of “Hey, I’m here too! Next!” is not interesting to us. Abomination is in a prison somewhere too.'"
Makes sense, and to be fair, Marvel hasn't re-used very many bad guys. I don't think we're getting a Ronan callback anytime soon, and none of Iron Man's foes have had repeat performances. But I think this has more to do with the Hulk not having a solo franchise. If that were to change then we might see these characters return, even if they are played by other actors.
