There has been two official images released for Marvel Studios’ Doctor Strange in the Multiverse of Madness.
Charlize Theron’s character was revealed at the end of the movie; as Clea. She is a powerful sorceress and lover to Doctor Strange in the comics.
Clea and Doctor Strange
There was also a second image posted via Charlize Theron’s Twitter account; of a close up of Clea.
Post Credit scene explained
Clea explains to Doctor Strange, that he has caused an Incursion. This is a phenomenon where the boundary between two universes breaks, causing one or both of the universes to be destroyed. Basically, leading up to an eventual Secret Wars movie.