User blog comment:Jacknapier10/Which characters cannot appear in the Marvel Cinematic Universe?/@comment-24901406-20140504155203

Which characters cannot appear? They have never actually bothered producing a list of characters, but there are four franchises as of the moment that are completely outwith Marvel Studios control:

X-Men (which includes pretty much everything mutant related adding up to 800 characters0 Fantastic Four Deadpool (gets his own franchise because he's special) Namor

There is also Spider-Man who is in a rather bizarre position because Sony completely bought out Marvel's stake in the production of the films but in the process of doing so sold off numerous other aspects of the deal including the live action television rights in 2009 so characters tied up in the Spider-Man franchise can appear so long as it isn't on film.

Additionally there are things that are shared between franchises like the Scarlet Witch, Quicksilver, the Kree and the Skrulls for example and things that are in the public domain (such as Atlantis) that are allowed even though other studios can also use them.

There is also another deal (after a lengthy legal battle) with Fox agreeing they will not use the word "mutant" as long as Fox hold the X-Men rights but this is NOT part of the rights package (so technically Sony could use it if they really wanted to take the same risks Marvel did when they produced Mutant X).