The Mistress of Mystery is a fictional character in the Fallout universe, a retro-futuristic post-apocalyptic video game franchise. She was created by the fictional Hubris Comics before the Great War of 2077 and intended to be the former lover and companion of the Silver Shroud, another fictional character created by Hubris Comics who terrorizes the criminals of Boston, Massachusetts. The Mistress of Mystery and Silver Shroud often appear together in the Unstoppables comic books that can be found scattered around the ruins of Boston after the nuclear war in 2077.

"She is shown to carry a .44 revolver called the Voice of Set on the Unstoppables covers and mentions using a weapon she calls the Blade of Bastet in the radio show. She's also an accomplished unarmed fighter, mostly relying on kicks. She wears long black gloves, a black evening gown with a white collar of several styles, and black heels. She tends to speak in alliteration. In Fallout 76, it is revealed that she used a phantom device for escapes," (Fallout Wiki).

Fictional voice actress Shannon Rivers portrayed the Mistress of Mystery on the radio show. When the world was destroyed by nuclear weapons during the Great War of 2077, Rivers, her husband, and her daughter survived. They founded the Order of Mysteries based on the ideals of the pre-war hero. The family adopted young orphaned girls and trained them to be able to defend themselves, expecting them to live up to the ideals of the Mistress of Mystery.