Lupita Nyong'o and Michael B. Jordan were huge gets for the Marvel's Black Panther, but their characters had remained somewhat of a mystery up until now.
Both have just had their roles announced during the Marvel panel though so you can stop wondering. Nyong'o is playing Nakia and Michael B. Jordan is taking on Erik Killmonger, who we can now assume is the main villain in the movie, I'd imagine. It was also announced that Danai Gurira is playing Okoye.
This is shaping up very nicely.