When asked yesterday by Marvel’s Lorraine Cink whether there would be Marvel characters in Age of Ultron who have not been seen in the preview photos, characters that have been in other films or in other as yet un-filmed corners of the Marvel Universe, Joss Whedon said simply, "Yes," without giving the slightest clues as to who the so-far-unseen characters are.

Concept Art for the Black Panther Movie

Of course there are some characters who names have been on already released posters, who haven’t been seen in the promos, notably Anthony Mackie (Falcon) and Hayley Atwell (Peggy Carter), but speculation is rampant that Chadwick Boseman, who has been announced as T-Challa in Marvel’s Black Panther film (see "'Black Panther,' 'Captain Marvel,' 'Inhumans' Movies"), might just make his first onscreen appearance in Age of Ultron, though it is likely we will have to wait until word leaks out from the first preview screenings to find out exactly who the characters that Whedon was referring to actually are.