What name did Beyoncé give her performance alter ego on her 2008 album?

Beyoncé called her performance alter ego Sasha Fierce.

The name became especially prominent with her 2008 double album I Am... Sasha Fierce. The album was divided into two discs: I Am..., which emphasized more personal songs, and Sasha Fierce, which focused on bolder, more performance-oriented material.

Beyoncé explained that Sasha Fierce represented the confident, energetic side of her stage persona. She later said that the alter ego helped her separate her private self from the demands of performing, although she eventually felt that the distinction was no longer necessary.

The album produced major hits including “If I Were a Boy,” “Single Ladies (Put a Ring on It),” and “Halo.” Sasha Fierce is therefore a character concept associated with an album era, not Beyoncé's legal name or a separate recording artist.