How many transfixing characters can one actress play in her career? Because whatever the estimate, Charlize Theron blew right past it a long time ago. Whether she's playing a determined detective or a post-apocalyptic road warrior, a serial killer or a news anchor, an evil fairy-tale queen or an immortal mercenary, Theron immerses herself completely, somehow becoming unrecognizable despite her famously stunning face. But while the end result tends to be the same—a critically acclaimed performance, hence the Oscar win and two other nominations—she has honed her approach to acting over the years, what used to work for her at 20 not necessarily making sense to her by...