Natalie Portman's Jane Foster is absent from the cast of Thor: Ragnarok, and according to Portman herself, that may be because she's "done" with Marvel movies.
"As far as I know, I'm done," Portman told the Wall Street Journal when asked if she would appear in any future films from Marvel. "I don't know if maybe one day they'll ask for Avengers 7 or whatever. I have no idea."
"As far as I know, I'm done, but it was a great thing to be a part of."
Portman's Foster was an Earthbound physicist and love interest for Chris Hemsworth's Thor in two films. In comic books, Jane Foster is more important to the Thor mythos than ever as the current wielder of Mjolnir.
Thor: Ragnarok is currently in production for a November 3, 2017 theatrical release.