Among the many different looks she has in the film are a soft-looking, all-business blonde and a raven-haired femme fatale who easily could be concealing a dagger or a gun.

Which is the real Salt? That's what filmmakers say is the central mystery.

"She's a character you never know," says Lorenzo di Bonaventura, who also produced Transformers and the upcoming G.I. Joe. "People who think they know the real her may or may not. Those who think they can tell whether she's in a disguise also may or may not.

"You're supposed to be kept guessing. She tells you her agenda, but are you supposed to believe it?"