Nathan Fillion has his role in Guardians of the Galaxy Vol. 2. Or rather, he's got quite a few roles... one in Oh, Rebecca, one as Tony Stark in a biopic on Tony Stark, and one as the hero in Arkon. That's right: Nathan Fillion is none other than Simon Williams, also known as Wonder Man. Wonder Man is made of ionic energy and is a long time Avenger, but his true passion is acting, something that earned him a fictional star on the Hollywood Walk of Fame.
Comicbook.com received several photos from Jonathan Hunter depicting a "Simon Williams Film Festival" at a movie theater. Though the site pointed out that its unlikely Wonder Man will be in action in the film, it's not impossible. Simon actually led an incarnation of the Guardians of the Galaxy under the name Hollywood.
So far, neither Fillion nor director James Gunn has commented on his inclusion.